From 79249345968fdf93852a9d6288e11ed512f00847 Mon Sep 17 00:00:00 2001
From: Karl Berry <karl@freefriends.org>
Date: Tue, 4 May 2021 22:31:00 +0000
Subject: latex-dev (5may21)

git-svn-id: svn://tug.org/texlive/trunk@59080 c570f23f-e606-0410-a88d-b1316a301751
---
 Master/texmf-dist/source/latex-dev/base/format.ins |    9 +-
 .../source/latex-dev/base/latexrelease.dtx         |  329 +++++-
 .../source/latex-dev/base/latexrelease.ins         |    7 +-
 Master/texmf-dist/source/latex-dev/base/letter.dtx |    4 +-
 Master/texmf-dist/source/latex-dev/base/ltbibl.dtx |    2 +-
 .../texmf-dist/source/latex-dev/base/ltboxes.dtx   |    4 +-
 .../texmf-dist/source/latex-dev/base/ltclass.dtx   |   91 +-
 Master/texmf-dist/source/latex-dev/base/ltcmd.dtx  |   68 +-
 .../source/latex-dev/base/ltcmdhooks.dtx           | 1093 ++++++++++++++++++
 .../texmf-dist/source/latex-dev/base/ltdefns.dtx   |    5 +-
 Master/texmf-dist/source/latex-dev/base/ltexpl.dtx |   37 +-
 .../source/latex-dev/base/ltfilehook.dtx           |   24 +-
 .../texmf-dist/source/latex-dev/base/ltfiles.dtx   |  145 ++-
 .../texmf-dist/source/latex-dev/base/ltfinal.dtx   |   73 +-
 .../texmf-dist/source/latex-dev/base/ltfloat.dtx   |   24 +-
 .../texmf-dist/source/latex-dev/base/ltfssaxes.dtx |   15 +-
 .../texmf-dist/source/latex-dev/base/ltfssbas.dtx  |   28 +-
 .../texmf-dist/source/latex-dev/base/ltfssini.dtx  |   58 +-
 .../texmf-dist/source/latex-dev/base/ltfsstrc.dtx  |   16 +-
 .../texmf-dist/source/latex-dev/base/lthooks.dtx   | 1186 +++++++++++++++-----
 .../texmf-dist/source/latex-dev/base/ltluatex.dtx  |    6 +-
 Master/texmf-dist/source/latex-dev/base/ltmath.dtx |    8 +-
 .../texmf-dist/source/latex-dev/base/ltmiscen.dtx  |    2 +-
 .../texmf-dist/source/latex-dev/base/ltoutenc.dtx  |   15 +-
 Master/texmf-dist/source/latex-dev/base/ltpar.dtx  |   16 +-
 Master/texmf-dist/source/latex-dev/base/ltpara.dtx |  381 ++++---
 .../texmf-dist/source/latex-dev/base/ltpictur.dtx  |    5 +-
 .../texmf-dist/source/latex-dev/base/ltplain.dtx   |  210 +++-
 .../texmf-dist/source/latex-dev/base/ltshipout.dtx |    8 +-
 Master/texmf-dist/source/latex-dev/base/lttab.dtx  |   10 +-
 .../source/latex-dev/base/lttextcomp.dtx           |   69 +-
 Master/texmf-dist/source/latex-dev/base/ltvers.dtx |  121 +-
 .../texmf-dist/source/latex-dev/graphics/color.dtx |    4 +-
 .../source/latex-dev/graphics/drivers.dtx          |    4 +-
 .../source/latex-dev/graphics/epsfig.dtx           |    4 +-
 .../source/latex-dev/graphics/graphics.dtx         |   19 +-
 .../source/latex-dev/graphics/graphicx.dtx         |   11 +-
 .../source/latex-dev/graphics/keyval.dtx           |    4 +-
 .../source/latex-dev/graphics/lscape.dtx           |    4 +-
 .../source/latex-dev/graphics/rotating.dtx         |    8 +-
 .../texmf-dist/source/latex-dev/graphics/trig.dtx  |    6 +-
 Master/texmf-dist/source/latex-dev/tools/array.dtx |    5 +-
 Master/texmf-dist/source/latex-dev/tools/bm.dtx    |   67 +-
 .../texmf-dist/source/latex-dev/tools/layout.dtx   |   14 +-
 .../source/latex-dev/tools/longtable.dtx           |   28 +-
 Master/texmf-dist/source/latex-dev/tools/trace.dtx |   30 +-
 46 files changed, 3470 insertions(+), 807 deletions(-)
 create mode 100644 Master/texmf-dist/source/latex-dev/base/ltcmdhooks.dtx

(limited to 'Master/texmf-dist/source/latex-dev')

diff --git a/Master/texmf-dist/source/latex-dev/base/format.ins b/Master/texmf-dist/source/latex-dev/base/format.ins
index 9c90555b9f3..eece2f57ef6 100644
--- a/Master/texmf-dist/source/latex-dev/base/format.ins
+++ b/Master/texmf-dist/source/latex-dev/base/format.ins
@@ -166,12 +166,14 @@ the system are in the document `cfgguide.tex'.
 % we have the extensions as soon as possible.
           \from{ltexpl.dtx}{2ekernel}         % expl3-based extensions
           \from{ltdefns.dtx}{2ekernel}
-          \from{ltcmd.dtx}{2ekernel}          % Used to be xparse
+          \from{ltcmd.dtx}{2ekernel}          % L3 layer module (used to be xparse)
           \from{lthooks.dtx}{2ekernel}        % L3 layer module
+          \from{ltcmdhooks.dtx}{2ekernel}     % L3 layer module
           \from{ltalloc.dtx}{2ekernel}
           \from{ltcntrl.dtx}{2ekernel}
           \from{lterror.dtx}{2ekernel}
           \from{ltpar.dtx}{2ekernel}
+          \from{ltpara.dtx}{2ekernel}         % L3 layer module
           \from{ltspace.dtx}{2ekernel}
           \from{ltlogos.dtx}{2ekernel}
           \from{ltfiles.dtx}{2ekernel}
@@ -240,11 +242,6 @@ the system are in the document `cfgguide.tex'.
 \generate{\file{structuredlog.sty}{\from{ltfilehook.dtx}{structuredlog}}}
 
 
-% hook managed para
-
-\generate{\file{ltpara.ltx}{\from{ltpara.dtx}{2ekernel}}}
-
-
 % luatex support (TeX part)
 
 \generate{\file{ltluatex.tex}{\from{ltluatex.dtx}{tex,plain}}}
diff --git a/Master/texmf-dist/source/latex-dev/base/latexrelease.dtx b/Master/texmf-dist/source/latex-dev/base/latexrelease.dtx
index cfcac4b3971..7d2290f4d8a 100644
--- a/Master/texmf-dist/source/latex-dev/base/latexrelease.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/latexrelease.dtx
@@ -37,13 +37,13 @@
 %<fixltx2e>\ProvidesPackage{fixltx2e}
 %<fixltx2e>   [2016/12/29 v2.1a fixes to LaTeX (obsolete)]
 %<latexrelease>\ProvidesPackage{latexrelease}
-%<*!fixltx2e>
+%<*latexrelease>
 % \fi
 %         \ProvidesFile{latexrelease.dtx}
-          [2021/01/23 v1.0l LaTeX release emulation and tests
+          [2021/04/29 v1.0n LaTeX release emulation and tests
               (including releases up to \latexreleaseversion)]
 % \iffalse
-%</!fixltx2e>
+%</latexrelease>
 %<*driver>
  \documentclass{ltxdoc}
  \newcommand\Lopt[1]{\textsf{#1}}
@@ -51,6 +51,8 @@
  \providecommand{\file}[1]{\texttt{#1}}
  \providecommand{\MF}{\textsf{Metafont}}
  \providecommand{\danger}{\marginpar[\hfill\protect\Huge!!]{\protect\Huge!!\hfill}}
+ \DeclareRobustCommand\cs[2][]{\texttt{\char`\\\detokenize{#2}}}
+ \DeclareRobustCommand\pkg[1]{\textsf{#1}}
  \begin{document}
  \DocInput{latexrelease.dtx}
  \end{document}
@@ -69,7 +71,7 @@
 % \title{The \Lpack{latexrelease} package\thanks{This file
 %         has version number \fileversion, last
 %         revised \filedate.}}
-% \author{The \LaTeX Project}
+% \author{The \LaTeX{} Project}
 % \date{\filedate}
 % \MaintainedByLaTeXTeam{latex}
 %  \maketitle
@@ -364,6 +366,99 @@
 % necessary as the new code only gets defined if that release is
 % chosen.
 %
+% \section{Declaring entire modules}
+%
+% Sometimes a large chunk of code is added as a module to another larger
+% code base.  As example of that in the 2020-10-01 release \LaTeX{} got
+% a new hook management system, \pkg{lthooks}, which was added in one go
+% and, as with all changes to the kernel, it was added to
+% \pkg{latexrelease}.  However rolling back from a future date to the
+% 2020-10-01 release didn't work because \pkg{latexrelease} would try to
+% define again all those commands, which would result in many
+% ``already defined'' errors and similar issues.
+%
+% To solve that problem, completely new modules can be defined in
+% \pkg{latexrelease} using the commands:
+% \begin{quote}
+%   \cs{NewModuleRelease}%^^A
+%     \verb|{|\meta{initial release date}%^^A
+%       \verb|}{|\meta{name}\verb|}{|\meta{message}\verb|}|\\
+%   \null\quad\meta{module code}\\
+%   \cs{IncludeInRelease}%^^A
+%     \verb|{0000/00/00}{|\meta{name}\verb|}{|\meta{message}\verb|}|\\
+%   \null\quad\meta{undefine module code}\\
+%   \cs{EndModuleRelease}
+% \end{quote}
+% With that setup, the module \meta{name} will be declared to exist only
+% in releases equal or later \meta{initial release date}.
+%
+% If \pkg{latexrelease} is rolling backwards or forwards between dates
+% after \meta{initial release date}, then all the \meta{module code} is
+% skipped, except when inside \meta{IncludeInRelease} guards, in which
+% case the code is applied or skipped as discussed above.
+%
+% If rolling forward from a date before the module's \meta{initial
+% release date} to a date after that, then all the \meta{module code} is
+% executed to define the module, and \cs{IncludeInRelease} guards are
+% executed accordingly, depending on the date declared and the target
+% date.
+%
+% If \pkg{latexrelease} is rolling back to a date before \meta{release
+% date}, then the code in the \cs{IncludeInRelease} guard dated
+% \verb|0000/00/00| is executed instead to undefine the module.  This
+% guard \emph{is not} ended by the usual \cs{EndIncludeInRelease}, but
+% instead by \cs{EndModuleRelease}.
+%
+% Finally, if rolling backwards or forwards between dates both before
+% \meta{initial release date}, the entire code between
+% \meta{NewModuleRelease} and \meta{EndModuleRelease} is entirely
+% skipped.
+%
+% \subsection{Example}
+%
+% Here is an example usage of the structure described above, as it would
+% be used in the \LaTeX{} kernel, taking \pkg{lthooks} as example:
+% \begin{verbatim}
+% %<*2ekernel|latexrelease>
+% \ExplSyntaxOn
+% %<latexrelease>\NewModuleRelease{2020/10/01}{lthooks}%
+% %<latexrelease>                 {The~hook~management~system}
+% \NewDocumentCommand \NewHook { m }
+%   { \hook_new:n {#1} }
+% %<latexrelease>\IncludeInRelease{2021/06/01}{\AddToHook}{Long~argument}
+% \NewDocumentCommand \AddToHook { m o +m }
+%   { \hook_gput_code:nnn {#1} {#2} {#3} }
+% %<latexrelease>\EndIncludeInRelease
+% %<latexrelease>
+% %<latexrelease>\IncludeInRelease{2020/10/01}{\AddToHook}{Long~argument}
+% %<latexrelease>\NewDocumentCommand \AddToHook { m o m }
+% %<latexrelease>  { \hook_gput_code:nnn {#1} {#2} {#3} }
+% %<latexrelease>\EndIncludeInRelease
+% %<latexrelease>
+% %<latexrelease>\IncludeInRelease{0000/00/00}{lthooks}{Undefine~lthooks}
+% %<latexrelease>\cs_undefine:N \NewHook
+% %<latexrelease>\cs_undefine:N \AddToHook
+% %<latexrelease>\EndModuleRelease
+% \ExplSyntaxOff
+% %</2ekernel|latexrelease>
+% \end{verbatim}
+%
+% In the example above, \cs{NewHook} is declared only once, and
+% unchanged in the next release (2021/06/01 in the example), so it has
+% no \cs{IncludeInRelease} guards, and will only be defined if needed.
+% \cs{AddToHook}, on the other hand, changed between the two releases
+% (made up for the example;  it didn't really happen)
+% and has an \cs{IncludeInRelease} block for the current release (off
+% \pkg{docstrip} guards, so it goes into the kernel too), and another
+% for the previous release (in \pkg{docstrip} guards so it goes only
+% into \pkg{latexrelease}).
+%
+% Note that in the example above, \cs{ExplSyntaxOn} and
+% \cs{ExplSyntaxOff} were added \emph{outside} the module code because,
+% as discussed above, sometimes the code outside \cs{IncludeInRelease}
+% guards may be skipped, but not the code inside them, and in that case
+% the catcodes would be wrong when defining the code.
+%
 % \section{fixltx2e}
 %
 % As noted above, prior to the 2015 \LaTeX\ release updates to the
@@ -387,27 +482,34 @@
 \NeedsTeXFormat{LaTeX2e}[1996/06/01]
 %    \end{macrocode}
 %
-% \section{Setup}
+% \subsection{Setup}
 %
 % \begin{macro}{\sourceLaTeXdate}
 %   \changes{v1.0l}{2021/01/23}{\cs{sourceLaTeXdate} added}
+%   \changes{v1.0m}{2021/03/18}{Define \cs{sourceLaTeXdate} conditionally}
 %   Store the original \LaTeX{} format version
-%   as a number in the format |YYYYMMDD|:
+%   as a number in the format |YYYYMMDD|.  This macro has to
+%   be defined conditionally, so that it isn't changed in case
+%   \file{latexrelease.sty} is loaded twice (for tests), but it
+%   can't be defined in the kernel only, otherwise
+%   \file{latexrelease.sty} wouldn't work in older \LaTeX{} due
+%   to the missing macro.
 %    \begin{macrocode}
-\edef\sourceLaTeXdate{%
-  \expandafter\@parse@version\fmtversion//00\@nil}
+\@ifundefined{sourceLaTeXdate}{%
+  \edef\sourceLaTeXdate{%
+    \expandafter\@parse@version\fmtversion//00\@nil}}{}%
 %    \end{macrocode}
 % \end{macro}
 %
 % \begin{macro}{\IncludeInRelease}
 % \begin{macro}{\EndIncludeInRelease}
-%    \begin{macrocode}
-%    \end{macrocode}
+%   These are defined in \file{ltvers.dtx}.
 % \end{macro}
 % \end{macro}
 %
 % \changes{v1.0c}{2015/02/19}{Swap argument order}
-% \changes{v1.0k}{2018/05/08}{reset \cs{\requestedLaTeXdate} for current and latest options, github issue 43}
+% \changes{v1.0k}{2018/05/08}{reset \cs{\requestedLaTeXdate} for current
+%                             and latest options, github issue 43}
 %    \begin{macrocode}
 \DeclareOption*{%
   \def\@IncludeInRelease#1[#2]{\@IncludeInRele@se{#1}}%
@@ -494,16 +596,213 @@ of this package available from CTAN}
 %    \end{macrocode}
 %
 %
-% \section{Individual  Changes}
+% \subsection{Ignoring \texttt{\string_new} errors when rolling back}
 %
-% The code for each change will be inserted at this point, extracted
-% from the kernel source files.
+% Enforce \cs{ExplSyntaxOn} and \cs{ExplSyntaxOff} to be \cs{relax} in
+% \pkg{latexrelease} if they are not yet defined.  They are later
+% restored to be undefined if needed.
+%    \begin{macrocode}
+\csname ExplSyntaxOn\endcsname
+\csname ExplSyntaxOff\endcsname
+%    \end{macrocode}
+%
+% \changes{v1.0m}{2021/03/18}
+%         {Make \texttt{\string_new} definitions harmless}
+%
+% Define a set of changes here, but we'll only use them later to make
+% sure they are applied after \pkg{expl3} is loaded.  If loading from a
+% rather old format, we don't have \cs{ExplSyntaxOn} yet.
+%    \begin{macrocode}
+\begingroup
+  \endlinechar=-1
+  \catcode95=11 % _
+  \catcode58=11 % :
+  \catcode126=10 % ~
+  \catcode32=09 % <space>
+  \xdef\latexrelease@postexpl{\unexpanded{%
+%<@@=latexrelease>
+%    \end{macrocode}
+%
+% First we'll define a \cs{declarecommand} that does \cs{renewcommand}
+% if the command being defined already exists, and \cs{newcommand}
+% otherwise.
+%    \begin{macrocode}
+\cs_gset_protected:Npn \@@_declare_command:w
+  { \@star@or@long \@@_declare_command:Nw }
+\cs_gset_protected:Npn \@@_declare_command:Nw #1
+  { \cs_if_exist:NTF #1 { \renew@command } { \new@command } #1 }
+%    \end{macrocode}
+%
+% Then define a version of \cs{e@alloc} that checks if the control
+% sequence being defined already exists, and if so, checks if its
+% meaning is the same as the one that would be defined with the call to
+% \cs{e@alloc}.  If both tests pass, nothing is defined to save a
+% register.  This version also takes care of setting
+% \cs{allocationnumber} to the value it would have after the register is
+% allocated.
+%    \begin{macrocode}
+\cs_gset_protected:Npn \@@_e@alloc:NnnnnN #1 #2 #3 #4 #5 #6
+  {
+    \cs_if_free:NTF #6
+      { \use:n }
+      {
+        \exp_after:wN \@@_e@alloc:N
+          \token_to_meaning:N #6 \scan_stop: {#2} #6
+      }
+        { \@@_e@alloc #1 {#2} {#3} {#4} {#5} #6 }
+  }
+%    \end{macrocode}
+% Walk through the meaning of the control sequence token by token,
+% looking for the register allocation number.
+%    \begin{macrocode}
+\cs_gset_protected:Npn \@@_e@alloc:N #1
+  {
+    \if_int_compare:w 0 < 0
+        \if_int_compare:w 10 < 9#1 ~ 1 \fi:
+        \if_charcode:w " #1 1 \fi: \exp_stop_f:
+      \tex_afterassignment:D \@@_e@alloc:w
+      \@tempcnta #1
+      \use_i:nnn
+    \fi:
+    \use:n
+      {
+        \if_meaning:w \scan_stop: #1
+          \exp_after:wN \use_iv:nnnn
+        \fi:
+        \@@_e@alloc:N
+      }
+  }
+%    \end{macrocode}
+% When found, check if it is the exact same register as it would be
+% allocated, and if it is, set \cs{allocationnumber} accordingly and
+% exit, otherwise undefine the register and allocate from scratch.
+%    \begin{macrocode}
+\cs_gset_protected:Npn \@@_e@alloc:w #1 \scan_stop: #2 #3
+  {
+    #2 \@@_tmp:w = \@tempcnta
+    \token_if_eq_meaning:NNTF #3 \@@_tmp:w
+      { \int_set_eq:NN \allocationnumber \@tempcnta  \use_none:n }
+      { \cs_set_eq:NN #3 \tex_undefined:D            \use:n      }
+  }
+%    \end{macrocode}
+%
+% Now create a token list to hold the list of changed commands, and
+% define a temporary macro that will loop through the command list,
+% store each in \cs{l_@@_restores_tl}, save a copy, and redefine each.
+%    \begin{macrocode}
+\tl_clear_new:N \l_@@_restores_tl
+\cs_gset:Npn \@@_tmp:w #1 #2
+  {
+    \quark_if_recursion_tail_stop_do:Nn #1
+      { \cs_undefine:N \@@_tmp:w }
+    \tl_put_right:Nn \l_@@_restores_tl {#1}
+    \cs_set_eq:cN { @@_ \cs_to_str:N #1 } #1
+    \cs_set_eq:NN #1 #2
+    \@@_tmp:w
+  }
+%    \end{macrocode}
 %
+% The redefinitions below are needed because:
+% \begin{description}
+%   \def\makelabel#1{\cs{#1}}
+%   \item[__kernel_chk_if_free_cs:N] This function is used ubiquitously
+%     in the \pkg{l3kernel} to check if a control sequence is definable,
+%     and give an error otherwise (similar to \cs{@ifdefinable}).
+%     Making it a no-op is enough for most cases (except when defining
+%     new registers);
+%   \item[e@alloc] In the case of new registers, we waste an allocation
+%     number if we do \cs[no-index]{new\meta{thing}} in a register
+%     that's already allocated, so the redefinition of \cs{e@alloc}
+%     checks if the new register is really necessary.  This code does
+%     not clear the register, which might cause problems in the future,
+%     if a register is allocated but not properly cleared before using;
+%   \item[__kernel_msg_error:nnx] This command is used to error on
+%     already defined scan marks.  Just making the error do nothing is
+%     enough, as no action is taken in that case;
+%   \item[msg_new:nnnn] Used to define new messages.  Making it
+%     \texttt{\string_gset} is enough.  Other msg commands like
+%     \cs{msg_new:nnn} and \cs[no-index]{__kernel_msg_new:nnn(n)} are
+%     defined in terms of \cs{msg_new:nnnn}, so there is no need to
+%     change the other ones;
+%   \item[NewDocumentCommand] Used to define user-level commands in the
+%     kernel.  Making it equal to \cs{DeclareDocumentCommand} solves the
+%     problem;
+%   \item[newcommand] Same as above.
+% \end{description}
+% And here we go:
+%    \begin{macrocode}
+\@@_tmp:w
+  \__kernel_chk_if_free_cs:N \use_none:n
+  \e@alloc \@@_e@alloc:NnnnnN
+  \__kernel_msg_error:nnx \use_none:nnn
+  \msg_new:nnnn \msg_gset:nnnn
+  \NewDocumentCommand \DeclareDocumentCommand
+  \newcommand \@@_declare_command:w
+%    \end{macrocode}
+%    Temp addition \ldots
 %    \begin{macrocode}
+  \__kernel_msg_error:nnn  \use_none:nnn  % needed while redirect for kernel msgs doesn't work
+  \q_recursion_tail \q_recursion_tail
+  \q_recursion_stop
+%    \end{macrocode}
+%
+% Finally, redirect the error thrown by \cs{NewHook} to nowhere so it
+% can be safely reused (the hook isn't redeclared if it already exists).
+%    \begin{macrocode}
+\msg_redirect_name:nnn { hooks } { exists } { none }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+  }}%
+\endgroup
 %</latexrelease>
 %    \end{macrocode}
 %
-% \section{fixltx2e}
+% \subsection{Undoing the temp modifications}
+%
+% If \cs{ExplSyntaxOn} exists (defined and not equal \cs{relax}), then
+% use the \pkg{expl3} restore code, otherwise restore \cs{ExplSyntaxOn}
+% and \cs{ExplSyntaxOff} to be undefined.
+%    \begin{macrocode}
+%<*latexrelease-finish>
+\@ifundefined{ExplSyntaxOn}%
+  {\let\ExplSyntaxOn\@undefined
+   \let\ExplSyntaxOff\@undefined
+   \@gobble}%
+  {\ExplSyntaxOn
+   \@firstofone}%
+  {%
+%    \end{macrocode}
+%
+% Now just loop through the list of redefined commands and restore their
+% previous meanings.
+%    \begin{macrocode}
+\tl_map_inline:Nn \l_@@_restores_tl
+  {
+    \cs_set_eq:Nc #1 { @@_ \cs_to_str:N #1 }
+    \cs_undefine:c { @@_ \cs_to_str:N #1 }
+  }
+\tl_clear:N \l_@@_restores_tl
+%    \end{macrocode}
+%
+% And restore the hook error message.
+%    \begin{macrocode}
+\msg_redirect_name:nnn { hooks } { exists } { }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%<@@=>
+  \ExplSyntaxOff}%
+%</latexrelease-finish>
+%    \end{macrocode}
+%
+% \subsection{Individual Changes}
+%
+% The code for each change will be inserted at this point, extracted
+% from the kernel source files.
+%
+%
+% \subsection{fixltx2e}
 %
 % Generate a stub \Lpack{fixltx2e} package:
 %    \begin{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/base/latexrelease.ins b/Master/texmf-dist/source/latex-dev/base/latexrelease.ins
index b4d0aef5677..0b65114a2f9 100644
--- a/Master/texmf-dist/source/latex-dev/base/latexrelease.ins
+++ b/Master/texmf-dist/source/latex-dev/base/latexrelease.ins
@@ -94,13 +94,15 @@ extension .ins) which are part of the distribution.
   \from{ltexpl.dtx}      {latexrelease}% empty 
   \from{ltdefns.dtx}     {latexrelease}%
   \from{ltcmd.dtx}       {latexrelease}%
-  \from{lthooks.dtx}     {latexrelease}% empty  % L3 layer module
+  \from{lthooks.dtx}     {latexrelease}% L3 layer module
+  \from{ltcmdhooks.dtx}  {latexrelease}% L3 layer module
   \from{ltalloc.dtx}     {latexrelease}% empty
   \from{ltcntrl.dtx}     {latexrelease}% empty
   \from{lterror.dtx}     {latexrelease}% empty
   \from{ltpar.dtx}       {latexrelease}% empty
+  \from{ltpara.dtx}      {latexrelease}% empty
   \from{ltspace.dtx}     {latexrelease}%
-  \from{ltlogos.dtx}     {latexrelease}% empty
+  \from{ltlogos.dtx}     {latexrelease}% L3 layer module
   \from{ltfiles.dtx}     {latexrelease}%
   \from{ltoutenc.dtx}    {latexrelease}%
   \from{ltcounts.dtx}    {latexrelease}%
@@ -133,6 +135,7 @@ extension .ins) which are part of the distribution.
   \from{ltoutput.dtx}    {latexrelease}%
   \from{ltfsscmp.dtx}    {latexrelease}% only in latexrelease!
   \from{ltfinal.dtx}     {latexrelease}%
+  \from{latexrelease.dtx}{latexrelease-finish}%
 }
 
 
diff --git a/Master/texmf-dist/source/latex-dev/base/letter.dtx b/Master/texmf-dist/source/latex-dev/base/letter.dtx
index 3c7fe56ba15..6beee81735a 100644
--- a/Master/texmf-dist/source/latex-dev/base/letter.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/letter.dtx
@@ -45,7 +45,7 @@
 %<*driver>
        \ProvidesFile{letter.drv}
 %</driver>
-              [2021/01/07 v1.3c
+              [2021/03/05 v1.3c
 %<+letter>               Standard LaTeX document class]
 %    \end{macrocode}
 %
@@ -1034,7 +1034,7 @@
 %    \texttt{extletter.cls},\\
 %    \texttt{frletter.cls},
 %    \texttt{hletter.cls},
-%    \texttt{scrlttr2.cls},
+%    \texttt{scrlttr2.cls} (change rejected),
 %    \texttt{lettre.cls},
 %    \texttt{beletter.cls},\\
 %    \texttt{brief.cls} and perhaps others.
diff --git a/Master/texmf-dist/source/latex-dev/base/ltbibl.dtx b/Master/texmf-dist/source/latex-dev/base/ltbibl.dtx
index 0319342dd49..cda0fa160ad 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltbibl.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltbibl.dtx
@@ -329,7 +329,7 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\nocite}{Allow nocite in preamble}%
 \def\nocite#1{\@bsphack
 %    \end{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/base/ltboxes.dtx b/Master/texmf-dist/source/latex-dev/base/ltboxes.dtx
index 8281b4b712b..8499d3ab8b9 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltboxes.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltboxes.dtx
@@ -464,7 +464,7 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\color@begingroup}{color group settings}%
 \let\color@begingroup\begingroup
 \def\color@endgroup{\endgraf\endgroup}
@@ -1140,7 +1140,7 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\@mpfootnotetext}{footnotetext tagging}%
 \long\def\@mpfootnotetext#1{%
   \global\setbox\@mpfootins\vbox{%
diff --git a/Master/texmf-dist/source/latex-dev/base/ltclass.dtx b/Master/texmf-dist/source/latex-dev/base/ltclass.dtx
index 26667cbeb1b..06b0e1cf43f 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltclass.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltclass.dtx
@@ -33,7 +33,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltclass.dtx}
-             [2021/02/18 v1.3x LaTeX Kernel (Class & Package Interface)]
+             [2021/03/27 v1.4a LaTeX Kernel (Class & Package Interface)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltclass.dtx}
@@ -640,14 +640,38 @@
 %<latexrelease>    \@expl@push@filename@aux@@}
 %<latexrelease>\EndIncludeInRelease
 %<latexrelease>
+%    \end{macrocode}
+%
+% When we roll back from a release that has \pkg{expl3} preloaded, the
+% definitions of \cs{@pushfilename} and \cs{@popfilename} can't be
+% completely rolled back otherwise \pkg{expl3}-based packages won't
+% have the automatic \cs{ExplSyntaxOff} at the end.  Here and below for
+% \cs{@popfilename}, we don't roll back all the way through if coming
+% from \LaTeX${}>2020-02-02$.
+% \changes{v1.4a}{2021/03/27}
+%         {Do not completely roll back if \pkg{expl3} is loaded.}
+%    \begin{macrocode}
 %<latexrelease>\IncludeInRelease{0000/00/00}{\@pushfilename}%
 %<latexrelease>  {Add \@expl@push@filename@@ and \@expl@push@filename@aux@@}%
+%<latexrelease>\ifnum\sourceLaTeXdate<20200202\relax
+%<latexrelease>  \GenericInfo{}{Defining 00-00-00\string\@pushfilename.}
 %<latexrelease>\def\@pushfilename{%
 %<latexrelease>  \xdef\@currnamestack{%
 %<latexrelease>    {\@currname}%
 %<latexrelease>    {\@currext}%
 %<latexrelease>    {\the\catcode`\@}%
 %<latexrelease>    \@currnamestack}}
+%<latexrelease>\else
+%<latexrelease>  \GenericInfo{}{Defining 2020-02-02\string\@pushfilename.}
+%<latexrelease>\def\@pushfilename{%
+%<latexrelease>  \@expl@push@filename@@
+%<latexrelease>  \xdef\@currnamestack{%
+%<latexrelease>    {\@currname}%
+%<latexrelease>    {\@currext}%
+%<latexrelease>    {\the\catcode`\@}%
+%<latexrelease>    \@currnamestack}%
+%<latexrelease>    \@expl@push@filename@aux@@}
+%<latexrelease>\fi
 %<latexrelease>\EndIncludeInRelease
 \@onlypreamble\@pushfilename
 %    \end{macrocode}
@@ -676,9 +700,21 @@
 %<latexrelease>  \@expl@pop@filename@@}
 %<latexrelease>\EndIncludeInRelease
 %<latexrelease>
+%    \end{macrocode}
+%
+% \changes{v1.4a}{2021/03/27}
+%         {Do not completely roll back if \pkg{expl3} is loaded.}
+%    \begin{macrocode}
 %<latexrelease>\IncludeInRelease{0000/00/00}{\@popfilename}%
 %<latexrelease>  {Add \@expl@push@filename@@ and \@expl@push@filename@aux@@}%
+%<latexrelease>\ifnum\sourceLaTeXdate<20200202\relax
+%<latexrelease>  \GenericInfo{}{Defining 00-00-00\string\@popfilename.}
 %<latexrelease>\def\@popfilename{\expandafter\@p@pfilename\@currnamestack\@nil}
+%<latexrelease>\else
+%<latexrelease>  \GenericInfo{}{Defining 2020-02-02\string\@popfilename.}
+%<latexrelease>\def\@popfilename{\expandafter\@p@pfilename\@currnamestack\@nil
+%<latexrelease>  \@expl@pop@filename@@}
+%<latexrelease>\fi
 %<latexrelease>\EndIncludeInRelease
 \@onlypreamble\@popfilename
 %    \end{macrocode}
@@ -1172,7 +1208,7 @@
 % \changes{v1.3x}{2021/02/18}{save raw option lists (gh/85)}
 %    \begin{macrocode}
 %</2ekernel>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\@pass@ptions}{Raw option lists}%
 %<*2ekernel|latexrelease>
 \def\@pass@ptions#1#2#3{%
@@ -1283,7 +1319,7 @@
 % unused options. Otherwise, in a package file do nothing.
 %    \begin{macrocode}
 %</2ekernel>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\OptionNotUsed}{filter unused option list}%
 %<*2ekernel|latexrelease>
 \def\@remove@eq@value#1=#2\@nil{#1}
@@ -1378,19 +1414,50 @@
 %
 % \changes{v0.2y}{1994/02/07}
 %         {Add extra ,s so `two' is not matched with `twocolumn'}
+% \changes{v1.3z}{2021/03/05}{modify so braces to not give errors (gh/513)}
 %    \begin{macrocode}
+%</2ekernel>
+%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>                 {\@xprocess@ptions}{safer @xprocess@ptions}%
+%<*2ekernel|latexrelease>
 \def\@xprocess@ptions{%
   \ifx\@currext\@clsextension\else
+   \ifx\@classoptionslist\relax\else
     \@for\CurrentOption:=\@classoptionslist\do{%
       \ifx\CurrentOption\@empty\else
-        \@expandtwoargs\in@{,\CurrentOption,}{,\@declaredoptions,}%
-        \ifin@
+        \@ifundefined{ds@\CurrentOption}{}{%
           \@use@ption
           \expandafter\let\csname ds@\CurrentOption\endcsname\@empty
-        \fi
+        }%
       \fi}%
+    \fi
   \fi
   \@process@pti@ns}
+%</2ekernel|latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{0000/00/00}%
+%<latexrelease>                 {\@xprocess@ptions}{safer @xprocess@ptions}%
+%<latexrelease>\let\@remove@eq@value\@undefined
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%<latexrelease>\def\@xprocess@ptions{%
+%<latexrelease>  \ifx\@currext\@clsextension\else
+%<latexrelease>    \@for\CurrentOption:=\@classoptionslist\do{%
+%<latexrelease>      \ifx\CurrentOption\@empty\else
+%<latexrelease>        \@expandtwoargs\in@{,\CurrentOption,}{,\@declaredoptions,}%
+%<latexrelease>        \ifin@
+%<latexrelease>          \@use@ption
+%<latexrelease>          \expandafter\let\csname ds@\CurrentOption\endcsname\@empty
+%<latexrelease>        \fi
+%<latexrelease>      \fi}%
+%<latexrelease>  \fi
+%<latexrelease>  \@process@pti@ns}
+%<latexrelease>\EndIncludeInRelease
+%<*2ekernel>
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 \@onlypreamble\@xprocess@ptions
 %    \end{macrocode}
 %
@@ -1472,7 +1539,7 @@
 % \changes{v1.3x}{2021/02/18}{filter out =value from unused option list (gh/85)}
 %    \begin{macrocode}
 %</2ekernel>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\@use@ption}{filter unused option list}%
 %<*2ekernel|latexrelease>
 \def\@use@ption{%
@@ -1954,7 +2021,7 @@
 %   \usepackage{some/local/path/array}
 %   \usepackage{array}
 % \end{verbatim}
-%    won't load \file{array.sty} twice.  It is remotely possible that
+%    won't load |array.sty| twice.  It is remotely possible that
 %    those are two different files, but as a matter of principles, we
 %    will consider that the base file name uniquely identifies a
 %    package, regardless of where it lives.  This assumption already
@@ -2669,15 +2736,15 @@
 %    this only works for input files ending in \texttt{.tex}. If a
 %    different extension is used there is no way to see that we are
 %    overwriting ourselves!
+% \changes{v1.3y}{2021/03/03}
+%         {Fix overwrite check for files with UTF-8 (gh/415)}
 %    \begin{macrocode}
-      \edef\reserved@a{#1}%
-      \edef\reserved@a{\detokenize\expandafter{\reserved@a}}%
       \edef\reserved@b{\detokenize\expandafter{\jobname}}%
-      \ifx\reserved@a\reserved@b%
+      \ifx\@curr@file\reserved@b%
         \@fileswtrue%
       \else%
         \edef\reserved@b{\reserved@b\detokenize{.tex}}%
-        \ifx\reserved@a\reserved@b
+        \ifx\@curr@file\reserved@b
           \@fileswtrue%
         \fi%
       \fi%
diff --git a/Master/texmf-dist/source/latex-dev/base/ltcmd.dtx b/Master/texmf-dist/source/latex-dev/base/ltcmd.dtx
index 26ce75224fb..fee555586da 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltcmd.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltcmd.dtx
@@ -34,14 +34,15 @@
 %%% From File: ltcmd.dtx
 %
 %    \begin{macrocode}
-\def\ltcmdversion{v1.0a}
-\def\ltcmddate{2021/01/21}
+\def\ltcmdversion{v1.0d}
+\def\ltcmddate{2021-04-19}
 %    \end{macrocode}
 %
 %<*driver>
 % \fi
 \ProvidesFile{ltcmd.dtx}
-  [2020-11-20 v1.0 LaTeX Kernel (Document commands)]
+  [\ltcmddate\space \ltcmdversion\space
+   LaTeX Kernel (Document commands)]
 % \iffalse
 \documentclass{l3doc}
 \GetFileInfo{ltcmd.dtx}
@@ -57,7 +58,7 @@
 %
 % \section{Creating document commands}
 %
-% \changes{v1.0}{2020-11-20}{Initial version derived from \texttt{xparse.dtx}}
+% \changes{v1.0a}{2020/11/20}{Initial version derived from \texttt{xparse.dtx}}
 %
 % Document commands should be created using the tools provided by this module:
 % \cs{NewDocumentCommand}, etc.\@, in almost all cases. This allows clean
@@ -78,6 +79,7 @@
 %</2ekernel>
 %    \end{macrocode}
 %
+% \changes{v1.0b}{2021/03/18}{Use \cs{NewModuleRelease}.}
 % \pkg{ltcmd} code contains an |^^@| character, which usually has
 % catcode~15, so \cs{IncludeInRelease} will break when this code is
 % being skipped, so we'll save the catcode of |^^@| to restore later:
@@ -85,12 +87,9 @@
 %<*2ekernel|latexrelease>
 %<latexrelease>\edef\@latexrelease@catcode@null{\the\catcode`\^^@ }
 %<latexrelease>\catcode`\^^@=12
-%<latexrelease>\IncludeInRelease{2021/05/01}%
-%<latexrelease>                 {\NewDocumentCommand}{Document commands}%
-%    \end{macrocode}
-%
-%    \begin{macrocode}
 \ExplSyntaxOn
+%<latexrelease>\NewModuleRelease{2020/10/01}{ltcmd}
+%<latexrelease>                 {Document~command~parser}%
 %    \end{macrocode}
 %
 % \subsection{Variables and constants}
@@ -3196,7 +3195,7 @@
 %    \begin{macrocode}
 \cs_new_protected:Npn \@@_get_arg_spec:NTF #1#2#3
   {
-    \@@_cmd_if_xparse:NTF #1
+    \__kernel_cmd_if_xparse:NTF #1
       {
         \tl_set:Nx \ArgumentSpecification { \tl_item:Nn #1 { 2 } }
         #2
@@ -3374,15 +3373,22 @@
 % \end{macro}
 % \end{macro}
 %
-% \begin{macro}{\@@_cmd_if_xparse:NTF}
+% \begin{macro}{\__kernel_cmd_if_xparse:NTF}
+% \changes{v1.0d}{2021/04/19}{Renamed \cs{__cmd_cmd_if_xparse:NTF} to
+%      \cs{__kernel_cmd_if_xparse:NTF} for cross-module usage}
 % \begin{macro}{\@@_cmd_if_xparse_aux:N}
-%   To determine whether the command is an \pkg{xparse} command check
-%   that its |arg_spec| is empty (this also excludes non-macros) and
-%   that its |replacement_spec| starts with either \cs{@@_start:nNNnnn}
-%   (non-expandable command) or \cs{@@_start_expandable:nNNNNn}
-%   (expandable command) or \cs{@@_start_env:nnnnn} (environment).
+%
+%    To determine whether the command is an \pkg{xparse} command check
+%    that its |arg_spec| is empty (this also excludes non-macros) and
+%    that its |replacement_spec| starts with either
+%    \cs{@@_start:nNNnnn} (non-expandable command) or
+%    \cs{@@_start_expandable:nNNNNn} (expandable command) or
+%    \cs{@@_start_env:nnnnn} (environment).
+%
+%    This conditional is needed in several kernel modules and is
+%    therefore has a kernel-internal name.
 %    \begin{macrocode}
-\cs_new_protected:Npn \@@_cmd_if_xparse:NTF #1
+\cs_new_protected:Npn \__kernel_cmd_if_xparse:NTF #1
   {
     \exp_args:Nf \str_case_e:nnTF
       {
@@ -4008,29 +4014,15 @@
 %    \end{macrocode}
 %
 %    \begin{macrocode}
-\ExplSyntaxOff
-%    \end{macrocode}
-%
-%    \begin{macrocode}
-%</2ekernel|latexrelease>
-%<latexrelease>\EndIncludeInRelease
-%<latexrelease>\catcode`\^^@=\@latexrelease@catcode@null\relax
-%<latexrelease>
-%<latexrelease>\IncludeInRelease{2020/10/01}%
-%<latexrelease>                 {\NewDocumentCommand}{Document commands}%
-%<latexrelease>\@ifundefined{NewDocumentCommand}
-%<latexrelease>  {%
-%<latexrelease>    \IfFileExists{xparse.ltx}
-%<latexrelease>      {\input xparse.ltx }
-%<latexrelease>      {\@latex@error{LaTeX requires xparse}\@ehd}%
-%<latexrelease>  }
-%<latexrelease>  {}
-%<latexrelease>\EndIncludeInRelease
 %<latexrelease>
-%<latexrelease>\IncludeInRelease{0000/00/00}%
-%<latexrelease>                 {\NewDocumentCommand}{Document commands}%
+%<latexrelease>\IncludeInRelease{0000/00/00}{ltcmd}%
+%<latexrelease>                 {Document~command~parser}%
 %<latexrelease>
-%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\EndModuleRelease
+\ExplSyntaxOff
+%<latexrelease>\@ifundefined{ExplSyntaxOff}{}{\latexrelease@postexpl}
+%<latexrelease>\catcode`\^^@=\@latexrelease@catcode@null\relax
+%</2ekernel|latexrelease>
 %    \end{macrocode}
 %
 % We need to stop DocStrip treating |@@| in a special way at this point.
diff --git a/Master/texmf-dist/source/latex-dev/base/ltcmdhooks.dtx b/Master/texmf-dist/source/latex-dev/base/ltcmdhooks.dtx
new file mode 100644
index 00000000000..cc67f5eaa75
--- /dev/null
+++ b/Master/texmf-dist/source/latex-dev/base/ltcmdhooks.dtx
@@ -0,0 +1,1093 @@
+% \iffalse meta-comment
+%
+%% File: ltcmdhooks.dtx (C) Copyright 2020-2021
+%%       Frank Mittelbach, Phelype Oleinik, LaTeX Team
+%
+% It may be distributed and/or modified under the conditions of the
+% LaTeX Project Public License (LPPL), either version 1.3c of this
+% license or (at your option) any later version.  The latest version
+% of this license is in the file
+%
+%    https://www.latex-project.org/lppl.txt
+%
+%
+%%% From File: ltcmdhooks.dtx
+%
+\def\ltcmdhooksversion{v1.0a}
+\def\ltcmdhooksdate{2021/04/30}
+%
+%
+%
+%<*driver>
+\documentclass{l3doc}
+%\usepackage{ltcmdhooks}
+\makeatletter
+\providecommand\footref[1]{%
+  \begingroup
+    \unrestored@protected@xdef\@thefnmark{\ref{#1}}%
+  \endgroup
+  \@footnotemark}
+\makeatother
+\EnableCrossrefs
+\CodelineIndex
+\begin{document}
+  \DocInput{ltcmdhooks.dtx}
+\end{document}
+%</driver>
+%
+% \fi
+%
+%
+% \providecommand\hook[1]{\texttt{#1}}
+% \providecommand\fmi[1]{\marginpar{\footnotesize FMi: #1}}
+% \providecommand\pho[1]{\marginpar{\footnotesize PhO: #1}}
+% \providecommand\phoinline[1]{\begin{quote}\itshape\footnotesize PhO: #1\end{quote}}
+%
+% \title{The \texttt{ltcmdhooks} module\thanks{This file has version
+%    \ltcmdhooksversion\ dated \ltcmdhooksdate, \copyright\ \LaTeX\
+%    Project.}}
+% \author{Frank Mittelbach \and Phelype Oleinik}
+%
+% \maketitle
+%
+%
+% \tableofcontents
+%
+%
+% \section{Introduction}
+%
+%    This file implements generic hooks for (arbitrary) commands.
+%    In theory every command \tn[no-index]{\meta{name}} offers now two
+%    associated hooks to which code can be added using \tn{AddToHook}
+%    or \tn{AddToHookNext}.\footnote{In practice this is not supported
+%    for all types of commands, see section~\ref{sec:look-ahead} for
+%    the restrictions that apply and what happens if one tries to use
+%    this with commands for which this is not supported.}  These are
+%    \begin{description}
+%    \item[\hook{cmd/\meta{name}/before}]
+%
+%       This hook is executed at the very start of the command
+%       execution after its arguments (if any) are parsed.  The hook
+%       \meta{code} is wrapped in the command inside a call to
+%       \cs{UseHook}|{cmd/|\meta{name}|/before}|, so the arguments
+%       passed to the command are \emph{not} available in the hook
+%       \meta{code}.
+%
+%    \item[\hook{cmd/\meta{name}/after}]
+%
+%       This hook is similar to \hook{cmd/\meta{name}/before}, but it is
+%       executed at the very end of the command body.  This hook is
+%       implemented as a reversed hook.
+%    \end{description}
+%
+%    The hooks are not physically present before
+%    \verb=\begin{document}= (i.e., using a command in the preamble
+%    will never execute them) and if nobody has declared any code for
+%    them, then they are not added to the command code ever.  For
+%    example, if we have the following definition
+%\begin{verbatim}
+%    \newcommand\foo[2]{Code #1 for #2!}
+%\end{verbatim}
+%    then executing \verb=\foo{A}{B}= will simply run
+%    \verb*=Code A for B!=
+%    as it was always the case. However, if somebody, somewhere (e.g.,
+%    in a package) adds
+%\begin{verbatim}
+%    \AddToHook{cmd/foo/before}{<before code>}
+%\end{verbatim}
+%    then, after |\begin{document}| the definition of \cs[no-index]{foo} will be:
+%\begin{verbatim}
+%    \renewcommand\foo[2]{\UseHook{cmd/foo/before}Code #1 for #2!}
+%\end{verbatim}
+%    and similarly \verb=\AddToHook{cmd/foo/after}{<after code>}=
+%    alters the definition to
+%\begin{verbatim}
+%    \renewcommand\foo[2]{Code #1 for #2!\UseHook{cmd/foo/after}}
+%\end{verbatim}
+%
+%    In other words, the mechanism is similar to what \pkg{etoolbox}
+%    offers with \tn{pretocmd} and \tn{apptocmd} with the important
+%    differences 
+%    \begin{itemize}
+%    \item
+%
+%      that code can be prepended or appended (i.e., added to the
+%      hooks) even if the command itself is not defined, because the
+%      defining package has not yet been loaded
+%
+%    \item
+%
+%      and that by using the hook management interface it is now
+%      possible to define how the code chunks added in these places
+%      are ordered, if different packages want to add code at these
+%      points.
+%
+%    \end{itemize}
+%
+%
+%
+%
+% \section{Restrictions and Operational details}
+% \label{sec:restrictions}
+%
+% Adding arbitrary material to commands is tricky because most of the
+% time we do not know what the macro expects as arguments when expanding
+% and \TeX{} doesn't have a reliable way to see that, so some guesswork
+% has to be employed.
+%
+% \subsection{Patching}
+%
+% The code here tries to find out if a command was defined with
+% \tn{newcommand} or \tn{DeclareRobustCommand} or
+% \tn{NewDocumentCommand}, and if so it \emph{assumes} that the argument
+% specification of the command is as expected (which is not fail-proof,
+% if someone redefines the internals of these commands in devious ways,
+% but is a reasonable assumption).
+%
+% If the command is one of the defined types, the code here does a
+% sandboxed expansion of the command such that it can be redefined again
+% exactly as before, but with the hook code added.
+%
+% If however the command is not a known type (it was defined with
+% \tn{def}, for example), then the code uses an approach similar to
+% \pkg{etoolbox}'s \tn{patchcmd} to retokenize the command with the hook
+% code in place.  This procedure, however, is more likely to fail if the
+% catcode settings are not the same as the ones at the time of command's
+% definition, so not always adding a hook to a command will work.
+%
+% \subsubsection{Timing}
+%
+% When \cs{AddToHook} (or its \pkg{expl3} equivalent) is called with
+% a generic |cmd| hook, say, \hook{cmd/foo/before}, for the first time
+% (that is, no code was added to that same hook before), in the preamble
+% of a document, it will store a patch instruction for that command
+% until |\begin{document}|, and only then all the commands which had
+% hooks added will be patched in one go.  That means that no command in
+% the preamble will have hooks patched into them.
+%
+% At |\begin{document}| all the delayed patches will be executed, and
+% if the command doesn't exist the code is still added to the hook,
+% but it will not be executed.  After |\begin{document}|, when
+% \cs{AddToHook} is called with a generic |cmd| hook the first time,
+% the command will be immediately patched to include the hook, and if
+% it doesn't exist or if it can't be patched for any reason, an error
+% is thrown; if \cs{AddToHook} was already used in the preamble no new
+% patching is attempted.
+%
+% This has the consequence that a command defined or redefined after
+% |\begin{document}| only uses generic |cmd| hook code if
+% \cs{AddToHook} is called for the first time after the definition is
+% made, or if the command explicitly uses the generic hook in its
+% definition by declaring it with \cs{NewHookPair} adding \cs{UseHook} as
+% part of the code.\footnote{We might change this behavior in the main
+% document slightly after gaining some usage experience.}
+%
+%
+% \subsection{Commands that look ahead}
+% \label{sec:look-ahead}
+%
+% Some commands are defined in different ``steps'' and they look ahead
+% in the input stream to find more arguments.  If you try to add some
+% code to the \hook{cmd/\meta{name}/after} hook of such command, it will
+% not work, and it is not possible to detect that programmatically, so
+% the user has to know (or find out) which commands can or cannot have
+% hooks attached to them.
+%
+% One good example is the \tn{section} command.  You can add something
+% to the \hook{cmd/section/before} hook, but if you try to add something
+% to the \hook{cmd/section/after} hook, \tn{section} will no longer
+% work.  That happens because the \tn{section} macro takes no argument,
+% but instead calls a few internal \LaTeX{} macros to look for the
+% optional and mandatory arguments.  By adding code to the
+% \hook{cmd/section/after} hook, you get in the way of that scanning.
+%
+%
+%
+% \section{Package Author Interface}
+%
+% The \hook{cmd} hooks are, by default, available for all commands
+% that can be patched to add the hooks.  For some commands, however,
+% the very beginning or the very end of the code is not the best place
+% to put the hooks, for example, if the command looks ahead for
+% arguments (see section~\ref{sec:look-ahead}).
+%
+% If you are a package author and you want to add the hooks to your
+% own commands in the proper position you can define the command and
+% manually add the \cs{UseHook} calls inside the command in the proper
+% positions, and manually define the hooks with \cs{NewHook} or
+% \cs{NewReversedHook}.  When the hooks are explicitly defined,
+% patching is not attempted so you can make sure your command works
+% properly.  For example, an (admittedly not really useful) command
+% that typesets its contents in a framed box with width optionally
+% given in parentheses:
+% \begin{verbatim}
+%    \newcommand\fancybox{\@ifnextchar({\@fancybox}{\@fancybox(5cm)}}
+%    \def\@fancybox(#1)#2{\fbox{\parbox{#1}{#2}}}
+% \end{verbatim}
+% If you try that definition, then add some code after it with
+% \begin{verbatim}
+%    \AddToHook{cmd/fancybox/after}{<code>}
+% \end{verbatim}
+% and then use the \cs[no-index]{fancybox} command you will see that it
+% will be completely broken, because the hook will get executed in the
+% middle of parsing for optional \texttt{(...)} argument.
+%
+% If, on the other hand, you want to add hooks to your command you can
+% do something like:
+% \begin{verbatim}
+%   \newcommand\fancybox{\@ifnextchar({\@fancybox}{\@fancybox(5cm)}}
+%   \def\@fancybox(#1)#2{\fbox{%
+%                        \UseHook{cmd/fancybox/before}%
+%                        \parbox{#1}{#2}%
+%                        \UseHook{cmd/fancybox/after}}}
+%   \NewHook{cmd/fancybox/before}
+%   \NewReversedHook{cmd/fancybox/after}
+% \end{verbatim}
+% then the hooks will be executed where they should and no patching
+% will be attempted.  It is important that the hooks are declared with
+% \cs{NewHook} or \cs{NewReversedHook}, otherwise the command hook
+% code will try to patch the command.  Note also that the call to
+% |\UseHook{cmd/fancybox/before}| does not need to be in the
+% definition of \cs[no-index]{fancybox}, but anywhere it makes sense
+% to insert it (in this case in the internal
+% \cs[no-index]{@fancybox}).
+%
+% Alternatively, if for whatever reason your command does not support
+% the generic hooks provided here, you can disable a hook with
+% \cs{DisableHook}\footnote{Please use \cs{DisableHook} if at all, only
+% on hooks that you \enquote{own}, i.e., for commands that your
+% package or class defines and not second guess
+% whether or not hooks of other packages should get disabled!}, so
+% that when someone tries to add code to it they will get an error.
+% Or if you don't want the error, you can simply declare the hook with
+% \cs{NewHook} and never use it.
+%
+%
+% The above approach is useful for really complex commands where for
+% one or the other reason the hooks can't be placed at the very
+% beginning and end of the command body and some hand-crafting is
+% needed. However, in the example above the real (and in fact only)
+% issue is the cascading argument parsing in the style developed long
+% ago in \LaTeX~2.09. Thus, a much simpler solution for this case is
+% to replace it with the modern \cs{NewDocumentCommand} syntax and
+% define the command as follows:
+% \begin{verbatim}
+%  \DeclareDocumentCommand\fancybox{D(){5cm}m}{\fbox{\parbox{#1}{#2}}}
+% \end{verbatim}
+% If you do that then both hooks automatically work and are patched
+% into the right places.
+%
+% \StopEventually{\setlength\IndexMin{200pt}  \PrintIndex  }
+%
+%
+%
+% \section{The Implementation}
+%
+% \subsection{Execution plan}
+%
+% To add |before| and |after| hooks to a command we will need to peek
+% into the definition of a command, which is always a tricky thing to
+% do.  Some cases are easy because we know how the command was defined,
+% so we can assume how its \meta{parameter text} looks like (for example
+% a command defined with \tn{newcommand} may have an optional argument
+% followed by a run of mandatory arguments), so we can just expand that
+% command and make it grab |#1|, |#2|, etc.\@ as arguments and
+% define it all back with the hooks added.
+%
+% Life's usually not that easy, so with some commands we can't do that
+% (a |#1| might as well be |#|$_{12}$|1|$_{12}$ instead of the expected
+% |#|$_{6}$|1|$_{12}$, for example) so we need to resort to ``patching''
+% the command: read its \tn{meaning}, and tokenize it again with
+% \tn{scantokens} and hope for the best.
+%
+% So the overall plan is:
+% \begin{enumerate}
+%   \item
+%     Check if a command is of a known type (that is, defined with
+%     \tn{newcommand}\footnote{It's not always possible to reliably
+%     detect this case because a command defined with no optional
+%     argument is indistinguishable from a \tn{def}ed command.},
+%     \cs[no-index]{DeclareRobustCommand}, or
+%     \cs[no-index]{New(Expandable)DocumentCommand}), and if is, take
+%     appropriate action.
+%   \item
+%     If the command is not a known type, we'll check if the command can
+%     be patched.  Two things will prevent a command from being
+%     patched:  if it was defined in a nonstandard catcode setting, or
+%     if it is an internal expl3 command with |__|\meta{module} in its
+%     name, in which case we refuse to patch.
+%   \item
+%     If the command was defined in nonstandard catcode settings, we
+%     will try a few standard ones to try our best to carry out the
+%     pathing.  If this doesn't help either, the code will give up and
+%     throw an error.
+% \end{enumerate}
+%
+%    \begin{macrocode}
+%<@@=hook>
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%<*2ekernel|latexrelease>
+\ExplSyntaxOn
+%<latexrelease>\NewModuleRelease{2021/06/01}{ltcmdhooks}
+%<latexrelease>                 {The~hook~management~system~for~commands}
+%    \end{macrocode}
+%
+% \subsection{Variables}
+%
+% \begin{macro}[int]{\g_hook_patch_action_list_tl}
+%    Pairs of |\if<cmd>..\patch<cmd>| to be used with
+%    \tn{robust@command@act} when looking for a known patching
+%    rule. This token list is exposed because we see some future
+%    applications (with very specialized packages, such as
+%    \pkg{etoolbox} that may want to extend the pairs processed. It is
+%    not meant for general use which is why it is not documented in
+%    the interface documentation above.
+%    \begin{macrocode}
+\tl_new:N \g_hook_patch_action_list_tl
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\l_@@_patch_num_args_int}
+%   The number of arguments in a macro being patched.
+%    \begin{macrocode}
+\int_new:N \l_@@_patch_num_args_int
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\l_@@_patch_prefixes_tl}
+% \begin{macro}{\l_@@_patch_param_text_tl}
+% \begin{macro}{\l_@@_patch_replacement_tl}
+%   The prefixes and parameters of the definition for the macro being
+%   patched.
+%    \begin{macrocode}
+\tl_new:N \l_@@_patch_prefixes_tl
+\tl_new:N \l_@@_patch_param_text_tl
+\tl_new:N \l_@@_patch_replacement_tl
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\g_@@_delayed_patches_prop}
+%   A list containing the patches delayed to |\begin{document}|, so that
+%   patching is not attempted twice.
+%    \begin{macrocode}
+\prop_new:N \g_@@_delayed_patches_prop
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_patch_debug:x}
+%   A helper for patching debug info.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_patch_debug:x #1
+  { \@@_debug:n { \iow_term:x { [lthooks]~#1 } } }
+%    \end{macrocode}
+% \end{macro}
+%
+% \subsection{Variants}
+%
+% \begin{macro}[int]{\tl_rescan:nV}
+%   \pkg{expl3} function variants used throughout the code.
+%    \begin{macrocode}
+\cs_generate_variant:Nn \tl_rescan:nn { nV }
+%    \end{macrocode}
+% \end{macro}
+%
+% \subsection{Patching or delaying}
+%
+% \begin{macro}{\@@_try_put_cmd_hook:n,\@@_try_put_cmd_hook:w}
+%   Before |\begin{document}| all patching is delayed.
+%   This function is called from within \cs{AddToHook}, when code is
+%   added to a generic |cmd| hook is newly declared.  It checks whether
+%   the patch position is valid, then proceeds to trying to patch or
+%   delaying to |\begin{document}| if in the preamble.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_try_put_cmd_hook:n #1
+  { \@@_try_put_cmd_hook:w #1 / / / \s_@@_mark {#1} }
+\cs_new_protected:Npn \@@_try_put_cmd_hook:w
+    #1 / #2 / #3 / #4 \s_@@_mark #5
+  {
+    \@@_debug:n { \iow_term:n { ->~Adding~cmd~hook~to~'#2'~(#3): } }
+    \str_case:nnTF {#3}
+        { { before } { } { after } { } }
+      { \exp_args:Nc \@@_patch_cmd_or_delay:Nnn {#2} {#2} {#3} }
+      { \__kernel_msg_error:nnn { hooks } { wrong-cmd-hook } {#2} {#3} }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+% \begin{macro}{\@@_patch_cmd_or_delay:Nnn}
+% \begin{macro}{\@@_cmd_begindocument_code:}
+%   In the preamble, \cs{@@_patch_cmd_or_delay:Nnn} just adds the patch
+%   instruction to a property list to be executed later.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_patch_cmd_or_delay:Nnn #1 #2 #3
+  {
+    \@@_debug:n { \iow_term:n { ->~Add~generic~cmd~hook~for~#2~(#3). } }
+    \@@_debug:n
+      { \iow_term:n { !~In~the~preamble:~delaying. } }
+    \prop_gput:Nnn \g_@@_delayed_patches_prop { #2 / #3 }
+      { \@@_cmd_try_patch:nn {#2} {#3} }
+  }
+%    \end{macrocode}
+%
+%   The delayed patches are added to a property list to prevent
+%   duplication, and the code stored in the property list for each
+%   key is executed.  The function \cs{@@_patch_cmd_or_delay:Nnn} is
+%   also redefined to be \cs{@@_patch_command:Nnn} so that no further
+%   delaying is attempted.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_cmd_begindocument_code:
+  {
+    \cs_gset_eq:NN \@@_patch_cmd_or_delay:Nnn \@@_patch_command:Nnn
+    \prop_map_function:NN \g_@@_delayed_patches_prop { \use_ii:nn }
+    \prop_gclear:N \g_@@_delayed_patches_prop
+    \cs_undefine:N \@@_cmd_begindocument_code:
+  }
+\g@addto@macro \@kernel@after@begindocument
+  { \@@_cmd_begindocument_code: }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\@@_cmd_try_patch:nn}
+%   At |\begin{document}| tries patching the command if the hook
+%   was not manually created in the meantime.  If the document does not
+%   exist, no error is raised here as it may hook into a package that
+%   wasn't loaded.  Hooks added to commands in the document body still
+%   raise an error if the command is not defined.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_cmd_try_patch:nn #1 #2
+  {
+    \@@_debug:n
+      { \iow_term:x { ->~\string\begin{document}~try~cmd / #1 / #2. } }
+    \@@_if_declared:nTF { cmd / #1 / #2 }
+      {
+        \@@_debug:n
+          { \iow_term:n { .->~Giving~up:~hook~already~created. } }
+      }
+      {
+        \cs_if_exist:cT {#1}
+          { \exp_args:Nc \@@_patch_command:Nnn {#1} {#1} {#2} }
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%
+%
+%
+%
+% \subsection{Patching commands}
+%
+% \begin{macro}{\@@_patch_command:Nnn}
+% \begin{macro}{\@@_patch_check:NNnn}
+% \begin{macro}[TF]{\@@_if_public_command:N}
+% \begin{macro}{\@@_if_public_command:w}
+%   \cs{@@_patch_command:Nnn} will do some sanity checks on the
+%   argument to detect if it is possible to add hooks to the command,
+%   and raises an error otherwise.  If the command can contain hooks,
+%   then it uses \tn{robust@command@act} to find out what type is the
+%   command, and patch it accordingly.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_patch_command:Nnn #1 #2 #3
+  {
+    \@@_patch_debug:x { analyzing~'\token_to_str:N #1' }
+    \@@_patch_debug:x { \token_to_str:N #1 = \token_to_meaning:N #1 }
+    \@@_patch_check:NNnn \cs_if_exist:NTF #1 { undef }
+      {
+        \@@_patch_debug:x { ++~control~sequence~is~defined }
+        \@@_patch_check:NNnn \token_if_macro:NTF #1 { macro }
+          {
+            \@@_patch_debug:x { ++~control~sequence~is~a~macro }
+            \@@_patch_check:NNnn \@@_if_public_command:NTF #1 { expl3 }
+              {
+                \@@_patch_debug:x { ++~macro~is~not~private }
+                \robust@command@act
+                  \g_hook_patch_action_list_tl #1
+                  \@@_retokenize_patch:Nnn { #1 {#2} {#3} }
+              }
+          }
+      }
+  }
+%    \end{macrocode}
+%
+%   And here's the auxiliary used above:
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_patch_check:NNnn #1 #2 #3 #4
+  {
+    #1 #2 {#4}
+      {
+        \__kernel_msg_error:nnxx { hooks } { cant-patch }
+          { \token_to_str:N #2 } {#3}
+      }
+  }
+%    \end{macrocode}
+%   and a conditional \cs{@@_if_public_command:N} to check if a command
+%   has |__| in its name (no other checking is performed).  Primitives
+%   with |:D| in their name could be included here, but they are already
+%   discarded in the \cs{token_if_macro:NTF} test above.
+%    \begin{macrocode}
+\use:x
+  {
+    \prg_new_protected_conditional:Npnn
+        \exp_not:N \@@_if_public_command:N ##1 { TF }
+      {
+        \exp_not:N \exp_last_unbraced:Nf
+          \exp_not:N \@@_if_public_command:w
+            { \exp_not:N \cs_to_str:N ##1 }
+          \tl_to_str:n { _ _ } \s_@@_mark
+      }
+  }
+\exp_last_unbraced:NNNNo
+\cs_new_protected:Npn \@@_if_public_command:w
+    #1 \tl_to_str:n { _ _ } #2 \s_@@_mark
+  {
+    \tl_if_empty:nTF {#2}
+      { \prg_return_true: }
+      { \prg_return_false: }
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+%
+%
+%
+%
+%
+%
+% \subsubsection{Patching by expansion and redefinition}
+%
+% \begin{macro}[int]{\g_hook_patch_action_list_tl}
+%    This is the list of known command types and the function that
+%    patches the command hooks into them.  The conditionals are taken
+%    from \tn{ShowCommand}, \tn{NewCommandCopy} and
+%    \cs{__kernel_cmd_if_xparse:NTF} defined in \texttt{ltcmd}.
+%    \begin{macrocode}
+\tl_gset:Nn \g_hook_patch_action_list_tl
+  {
+    { \@if@DeclareRobustCommand \@@_patch_DeclareRobustCommand:Nnn }
+    { \@if@newcommand \@@_patch_newcommand:Nnn }
+    { \__kernel_cmd_if_xparse:NTF \@@_cmd_patch_xparse:Nnn }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%
+%
+%
+% \begin{macro}{\@@_patch_DeclareRobustCommand:Nnn}
+%   At this point we know that the commands can be patched by expanding
+%   then redefining.  These are the cases of commands defined with
+%   \tn{newcommand} with an optional argument or with
+%   \tn{DeclareRobustCommand}.
+%
+%   With \cs{@@_patch_DeclareRobustCommand:Nnn} we check if the command
+%   has an optional argument (with a test counter-intuitively called
+%   \tn{@if@newcommand}).  If so, we forward the action to
+%   \cs{@@_patch_newcommand:Nnn}, otherwise call the patching engine
+%   \cs{@@_patch_expand_redefine:NNnn} with a \cs{c_false_bool} to
+%   indicate that there is no optional argument.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_patch_DeclareRobustCommand:Nnn #1
+  {
+    \exp_args:Nc \@if@newcommand { \cs_to_str:N #1 ~ }
+      { \exp_args:Nc \@@_patch_newcommand:Nnn }
+      { \exp_args:NNc \@@_patch_expand_redefine:NNnn \c_false_bool }
+        { \cs_to_str:N #1 ~ }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \begin{macro}{\@@_patch_newcommand:Nnn}
+%   If the command was defined with \tn{newcommand} and an optional
+%   argument, call the patching engine with a \cs{c_true_bool} to flag
+%   the presence of an optional argument, and with
+%   \cs[no-index]{\string\command} to patch the actual code for
+%   \cs[no-index]{command}.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_patch_newcommand:Nnn #1
+  {
+    \exp_args:NNc \@@_patch_expand_redefine:NNnn \c_true_bool
+      { \c_backslash_str \cs_to_str:N #1 }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%  \begin{macro}{\@@_cmd_patch_xparse:Nnn}
+%    And for commands defined by the \pkg{xparse} commands use this
+%    for patching:
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_cmd_patch_xparse:Nnn #1
+  {
+    \exp_args:NNc \@@_patch_expand_redefine:NNnn \c_false_bool
+      { \cs_to_str:N #1 ~ code }
+  }
+%    \end{macrocode}
+%  \end{macro}
+%
+%
+%
+%
+% \begin{macro}{\@@_patch_expand_redefine:NNnn}
+% \begin{macro}[EXP]{\@@_make_prefixes:w}
+%   Now the real action begins.  Here we have in |#1| a boolean
+%   indicating if the command has a |[|\ldots|]|-delimited argument, in
+%   |#2| the command control sequence, in |#3| the name of the command
+%   (note that |#1|${}\ne{}$|\csname#2\endcsname| at this point!), and
+%   in |#4| the hook position, either |before| or |after|.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_patch_expand_redefine:NNnn #1 #2 #3 #4
+  {
+    \@@_patch_debug:x { ++~command~can~be~patched~without~rescanning }
+%    \end{macrocode}
+%   We'll start by counting the number of arguments in the command by
+%   counting the number of characters in the \cs{cs_argument_spec:N} of
+%   the macro, divided by two, and subtracting one if the command has an
+%   optional argument (that is, an extra |[]| in its
+%   \meta{parameter text}).
+%    \begin{macrocode}
+    \int_set:Nn \l_@@_patch_num_args_int
+      {
+        \exp_args:Nf \str_count:n { \cs_argument_spec:N #2 } / 2
+        \bool_if:NT #1 { -1 }
+      }
+%    \end{macrocode}
+%   Now build two token lists:
+%   \begin{description}
+%     \item[\cs{l_@@_patch_param_text_tl}] will contain the
+%       \meta{parameter text} to be used when redefining the macro.  It
+%       should be identical to the \meta{parameter text} used when
+%       originally defining that macro.
+%     \item[\cs{l_@@_patch_replacement_tl}] will contain braced pairs of
+%       |#|$_{12}$\meta{num} to feed to the macro when expanded.  This
+%       token list as well as the previous will have the first item
+%       surrounded by |[|\ldots|]| in the case of an optional argument.
+%   \end{description}
+%    \begin{macrocode}
+    \int_compare:nNnTF { \l_@@_patch_num_args_int } > { \c_zero_int }
+      {
+        \tl_set:Nx \l_@@_patch_param_text_tl
+          { \bool_if:NTF #1 { [####1] } {  ####1  } }
+        \tl_set:Nx \l_@@_patch_replacement_tl
+          { \bool_if:NTF #1 { [####1] } { {####1} } }
+        \int_step_inline:nnn { 2 } { \l_@@_patch_num_args_int }
+          {
+            \tl_put_right:Nn \l_@@_patch_param_text_tl    { ## ####1 }
+            \tl_put_right:Nn \l_@@_patch_replacement_tl { { ## ####1 } }
+          }
+      }
+      {
+        \tl_clear:N \l_@@_patch_param_text_tl
+        \tl_clear:N \l_@@_patch_replacement_tl
+      }
+%    \end{macrocode}
+%   Finally, before redefining, we need to also get the prefixes used
+%   when defining the command.  Here we ensure that the \tn{escapechar}
+%   is printable, otherwise a macro defined with prefixes
+%   |\protected \long| will have it \tn{meaning} printed as
+%   |protectedlong|, making life unnecessarily complicated.  Here the
+%   \tn{escapechar} is changed to |/|, then we loop between pairs of
+%   |/|\ldots|/| extracting the prefixes.
+%    \begin{macrocode}
+    \group_begin:
+      \int_set:Nn \tex_escapechar:D { `\/ }
+      \use:x
+        {
+    \group_end:
+    \tl_set:Nx \exp_not:N \l_@@_patch_prefixes_tl
+      { \exp_not:N \@@_make_prefixes:w \cs_prefix_spec:N #2 / / }
+        }
+%    \end{macrocode}
+%   Now that all the needed tools are ready, without further ado we'll
+%   redefine the command |#2|.  The definition uses the prefixes
+%   gathered in \cs{l_@@_patch_prefixes_tl}, a primitive \cs{tex_def:D}
+%   to avoid adding extra prefixes, and the \meta{parameter text} from
+%   \cs{l_@@_patch_param_text_tl}.
+%
+%   Then finally, in the body of the definition, we insert
+%   \hook{cmd/\#3/before} if |#4| is |before|, the code of the
+%   command expanded once grabbing the parameters in
+%   \cs{l_@@_patch_replacement_tl}, and \hook{cmd/\#3/after} if |#4| is
+%   |after|.
+%    \begin{macrocode}
+    \use:x
+      {
+        \l_@@_patch_prefixes_tl \tex_def:D
+            \exp_not:N #2 \exp_not:V \l_@@_patch_param_text_tl
+          {
+            \str_if_eq:nnT {#4} { before }
+              { \exp_not:N \UseHook { cmd / #3 / #4 } }
+            \exp_args:No \exp_not:o
+              { \exp_after:wN #2 \l_@@_patch_replacement_tl }
+            \str_if_eq:nnT {#4} { after }
+              { \exp_not:N \UseHook { cmd / #3 / #4 } }
+          }
+      }
+  }
+%    \end{macrocode}
+%
+%   Here's the auxiliary that makes the prefix control sequences for the
+%   redefinition.  Each item has to be \cs{tl_trim_spaces:n}'d because
+%   the last item (and not any other) has a trailing space.
+%    \begin{macrocode}
+\cs_new:Npn \@@_make_prefixes:w / #1 /
+  {
+    \tl_if_empty:nF {#1}
+      {
+        \exp_not:c { tex_ \tl_trim_spaces:n {#1} :D }
+        \@@_make_prefixes:w /
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+%
+%
+%
+%
+%
+%
+% \subsubsection{Patching by retokenization}
+%
+% At this point we've drained the possibilities of patching a command by
+% expansion-and-redefinition, so we have to resort to patching by
+% retokenizing the command.  Patching by retokenization is done by
+% getting the \tn{meaning} of the command, doing the necessary
+% manipulations on the generated string, and the retokenizing that again
+% by using \tn{scantokens}.
+%
+% Patching by retokenization is definitely a riskier business, because
+% it relies that the tokens printed by \tn{meaning} produce the exact
+% same tokens as the ones in the original definition.  That is, the
+% catcode régime must be exactly(ish) the same, and there is no way of
+% telling except by trial and error.
+%
+% \begin{macro}{\@@_retokenize_patch:Nnn}
+%   This is the macro that will control the whole process.  First we'll
+%   try out one final, rather trivial case, of a command with no
+%   arguments;  that is, a token list.  This case can be patched with
+%   the expand-and-redefine routine but it has to be the very last case
+%   tested for, because most (all?) robust commands start with a
+%   top-level macro with no arguments, so testing this first would
+%   short-circuit \tn{robust@command@act} and the top-level macros would
+%   be incorrectly patched.  In that case, we just check if the
+%   \cs{cs_argument_spec:N} is empty, and call
+%   \cs{@@_patch_expand_redefine:NNnn}.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_retokenize_patch:Nnn #1 #2 #3
+  {
+    \@@_patch_debug:x { ..~command~can~only~be~patched~by~rescanning }
+    \str_if_eq:eeTF { \cs_argument_spec:N #1 } { }
+      { \@@_patch_expand_redefine:NNnn \c_false_bool #1 {#2} {#3} }
+      {
+%    \end{macrocode}
+%
+%   Otherwise, we start the actual patching by retokenization job.  The
+%   code calls \cs{@@_try_patch_with_catcodes:Nnnnw} with a different
+%   catcode setting:
+%   \begin{itemize}
+%     \item The current catcode setting;
+%     \item Switching the catcode of |@|;
+%     \item Switching the \pkg{expl3} syntax on or off;
+%     \item Both of the above.
+%   \end{itemize}
+%
+%   If patching succeeds, \cs{@@_try_patch_with_catcodes:Nnnnw} has the
+%   side-effect of patching the macro |#1| (which may be an internal
+%   from the command whose name is~|#2|).
+%    \begin{macrocode}
+        \tl_set:Nx \l_@@_tmpa_tl
+          {
+            \int_compare:nNnTF { \char_value_catcode:n {`\@ } } = { 12 }
+              { \exp_not:N \makeatletter } { \exp_not:N \makeatother }
+          }
+        \tl_set:Nx \l_@@_tmpb_tl
+          {
+            \bool_if:NTF \l__kernel_expl_bool
+              { \ExplSyntaxOff } { \ExplSyntaxOn }
+          }
+        \use:x
+          {
+            \exp_not:N \@@_try_patch_with_catcodes:Nnnnw
+                \exp_not:n { #1 {#2} {#3} }
+              { \prg_do_nothing: }
+              { \exp_not:V \l_@@_tmpa_tl } % @
+              { \exp_not:V \l_@@_tmpb_tl } % _:
+              {
+                \exp_not:V \l_@@_tmpa_tl   % @
+                \exp_not:V \l_@@_tmpb_tl   % _:
+              }
+          }
+              \q_recursion_tail \q_recursion_stop
+%    \end{macrocode}
+%
+%   If no catcode setting succeeds, give up and raise an error.  The
+%   command isn't changed in any way in that case.
+%    \begin{macrocode}
+          {
+            \__kernel_msg_error:nnxx { hooks } { cant-patch }
+              { \c_backslash_str #2 } { retok }
+          }
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \begin{macro}{\@@_try_patch_with_catcodes:Nnnnw}
+%   This function is a simple wrapper around
+%   \cs{@@_cmd_if_scanable:NnTF} and \cs{@@_patch_retokenize:Nnnn} if
+%   the former returns \meta{true}, plus some debug messages.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_try_patch_with_catcodes:Nnnnw #1 #2 #3 #4
+  {
+    \quark_if_recursion_tail_stop_do:nn {#4} { \use:n }
+    \@@_patch_debug:x { ++~trying~to~patch~by~retokenization }
+    \@@_cmd_if_scanable:NnTF {#1} {#4}
+      {
+        \@@_patch_debug:x { ++~macro~can~be~retokenized~cleanly }
+        \@@_patch_debug:x { ==~retokenizing~macro~now }
+        \@@_patch_retokenize:Nnnn #1 {#2} {#3} {#4}
+        \use_i_delimit_by_q_recursion_stop:nw \use_none:n
+      }
+      {
+        \@@_patch_debug:x { --~macro~cannot~be~retokenized~cleanly }
+        \@@_try_patch_with_catcodes:Nnnnw #1 {#2} {#3}
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%
+%
+%
+% \begin{macro}[int]{\kerneltmpDoNotUse}
+%   This is an oddity required to be safe (as safe as reasonably
+%   possible) when patching the command.  The entirety of
+%   \begin{quote}
+%     \meta{prefixes} \tn{def} \meta{cs} \meta{parameter text}
+%       |{|\meta{replacement text}|}|
+%   \end{quote}
+%   will go through \tn{scantokens}.  The \meta{parameter text} and
+%   \meta{replacement text} are what we are trying to retokenize, so not
+%   much worry there.  The other items, however, should ``just work'',
+%   so some care is needed to not use too fancy catcode settings.
+%   Therefore we can't use an \pkg{expl3}-named macro for \meta{cs}, nor
+%   the \pkg{expl3} versions of \tn{def} or the \meta{prefixes}.
+%   That is why the definitions that will eventually go into
+%   \tn{scantokens} will use the oddly (but hopefully clearly)-named
+%   \cs{kerneltmpDoNotUse}:
+%    \begin{macrocode}
+\cs_new_eq:NN \kerneltmpDoNotUse !
+%    \end{macrocode}
+%   \phoinline{Maybe this can be avoided by running the \meta{parameter text}
+%     and the \meta{replacement text} separately through \tn{scantokens}
+%     and then putting everything together at the end.}
+% \end{macro}
+%
+%
+%
+% \begin{macro}{\@@_patch_required_catcodes:}
+%   Here are the catcode settings that are \emph{mandatory} when
+%   retokenizing commands.  These are the minimum necessary settings to
+%   perform the definitions:  they identify control sequences, which
+%   must be escaped with |\|$_0$, delimit the definition with |{|$_1$
+%   and |}|$_2$, and mark parameters with |#|$_6$.  Everything else may
+%   be changed, but not these.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_patch_required_catcodes:
+  {
+    \char_set_catcode_escape:N \\
+    \char_set_catcode_group_begin:N \{
+    \char_set_catcode_group_end:N \}
+    \char_set_catcode_parameter:N \#
+    % \int_set:Nn \tex_endlinechar:D { -1 }
+    % \int_set:Nn \tex_newlinechar:D { -1 }
+  }
+%    \end{macrocode}
+%   \phoinline{\pkg{etoolbox} sets the \tn{endlinechar} and \tn{newlinechar}
+%     when patching, but as far as I tested these didn't make much of
+%     a difference, so I left them out for now.  Maybe
+%     \tn{newlinechar}|=-1| avoids a space token being added after the
+%     definition.}
+%   \phoinline{If the patching is split by \meta{parameter text} and
+%     \meta{replacement text}, then only \# will have to stay in that
+%     list.}
+%   \phoinline{Actually now that we patch
+%     \texttt{\cs{UseHook}\{cmd/foo/before\}}, all the tokens there need
+%     to have the right catcodes, so this list now includes all
+%     lowercase letters, U and H, the slash, and whatever characters in
+%     the command name\ldots sigh\ldots}
+% \end{macro}
+%
+%
+%
+%
+% \begin{macro}[TF]{\@@_cmd_if_scanable:Nn}
+%   Here we'll do a quick test if the command being patched can in fact
+%   be retokenized with the specific catcode setting without changing
+%   in meaning.  The test is straightforward:
+%   \begin{enumerate}
+%     \item apply \tn{meaning} to the command;
+%     \item split the \meta{prefixes}, \meta{parameter text} and
+%       \meta{replacement text} and arrange them as
+%       \begin{quote}
+%         \meta{prefixes}\tn{def}\cs{kerneltmpDoNotUse}%^^A
+%           \meta{parameter text}|{|\meta{replacement text}|}|
+%       \end{quote}
+%     \item rescan that with the given catcode settings, and do
+%       the definition; then finally
+%     \item compare \cs{kerneltmpDoNotUse} with the original command.
+%   \end{enumerate}
+%   If both are \tn{ifx}-equal, the command can be safely patched.
+%    \begin{macrocode}
+\prg_new_protected_conditional:Npnn \@@_cmd_if_scanable:Nn #1 #2 { TF }
+  {
+    \cs_set_eq:NN \kerneltmpDoNotUse \scan_stop:
+    \cs_set_eq:NN \@@_tmp:w \scan_stop:
+    \use:x
+      {
+        \cs_set:Npn \@@_tmp:w
+            ####1 \tl_to_str:n { macro: } ####2 -> ####3 \s_@@_mark
+          { ####1 \def \kerneltmpDoNotUse ####2   {####3} }
+        \tl_set:Nx \exp_not:N \l_@@_tmpa_tl
+          { \exp_not:N \@@_tmp:w \token_to_meaning:N #1 \s_@@_mark }
+      }
+    \tl_rescan:nV { #2 \@@_patch_required_catcodes: } \l_@@_tmpa_tl
+    \token_if_eq_meaning:NNTF #1 \kerneltmpDoNotUse
+      { \prg_return_true: }
+      { \prg_return_false: }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%
+%
+% \begin{macro}{\@@_patch_retokenize:Nnnn}
+%   Then, if \cs{@@_cmd_if_scanable:NnTF} returned true, we can go on
+%   and patch the command.
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_patch_retokenize:Nnnn #1 #2 #3 #4
+  {
+%    \end{macrocode}
+%   Start off by making some things \tn{relax} to avoid lots of
+%   \tn{noexpand} below.
+%    \begin{macrocode}
+    \cs_set_eq:NN \kerneltmpDoNotUse \scan_stop:
+    \cs_set_eq:NN \@@_tmp:w \scan_stop:
+    \use:x
+      {
+%    \end{macrocode}
+%   Now we'll define \cs{@@_tmp:w} such that it splits the \tn{meaning}
+%   of the macro (|#1|) into its three parts:
+%   \begin{enumerate}
+%     \def\makelabel#1{\texttt{\#\#\#\##1}}
+%     \item \meta{prefixes}
+%     \item \meta{parameter text}
+%     \item \meta{replacement text}
+%   \end{enumerate}
+%   and arrange that a complete definition, then place the |before|
+%   or |after| hooks around the \meta{replacement text}:
+%   accordingly.
+%    \begin{macrocode}
+        \cs_set:Npn \@@_tmp:w
+            ####1 \tl_to_str:n { macro: } ####2 -> ####3 \s_@@_mark
+          {
+            ####1 \def \kerneltmpDoNotUse ####2
+              {
+                \str_if_eq:nnT {#3} { before }
+                  { \token_to_str:N \UseHook { cmd / #2 / #3 } }
+                ####3
+                \str_if_eq:nnT {#3} { after }
+                  { \token_to_str:N \UseHook { cmd / #2 / #3 } }
+              }
+          }
+%    \end{macrocode}
+%   Now we just have to get the \tn{meaning} of the command being
+%   patched and pass it through the meat grinder above.
+%    \begin{macrocode}
+        \tl_set:Nx \exp_not:N \l_@@_tmpa_tl
+          { \exp_not:N \@@_tmp:w \token_to_meaning:N #1 \s_@@_mark }
+      }
+%    \end{macrocode}
+%   Now rescan with the given catcode settings (overridden by the
+%   \cs{@@_patch_required_catcodes:}), and implicitly (by using the
+%   rescanned token list) carry out the definition from above.
+%    \begin{macrocode}
+    \tl_rescan:nV { #4 \@@_patch_required_catcodes: } \l_@@_tmpa_tl
+%    \end{macrocode}
+%   And to close, copy the newly-defined command into the old name and
+%   the patching is finally completed:
+%    \begin{macrocode}
+    \cs_set_eq:NN #1 \kerneltmpDoNotUse
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+% \subsection{Messages}
+%
+%    \begin{macrocode}
+\__kernel_msg_new:nnnn { hooks } { wrong-cmd-hook }
+  {
+    Command~hook~`cmd/#1/#2'~invalid.\\
+    The~hook~should~be~`cmd/#1/before'~or~`cmd/#1/after'.
+  }
+  {
+    You~tried~to~add~a~hook~to~command~\iow_char:N \\#1,~but~`#2'~
+    is~an~invalid~position.~Only~`before'~or~`after'~are~allowed.
+  }
+\__kernel_msg_new:nnnn { hooks } { cant-patch }
+  {
+    Command~`#1'~cannot~have~hooks~because~it~
+    \@@_unpatchable_cases:n {#2} .
+  }
+  {
+    You~tried~to~add~a~hook~to~`#1',~but~LaTeX~was~not~able~to~
+    add~the~hook~to~that~command~because~`#1'~
+    \@@_unpatchable_cases:n {#2} .
+  }
+\cs_new:Npn \@@_unpatchable_cases:n #1
+  {
+    \str_case:nn {#1}
+      {
+        { undef } { doesn't~exist }
+        { macro } { is~not~a~macro }
+        { expl3 } { is~a~private~expl3~macro }
+        { retok } { can't~be~retokenized~cleanly }
+      }
+  }
+%    \end{macrocode}
+%
+%
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{0000/00/00}{ltcmdhooks}%
+%<latexrelease>                 {The~hook~management~system~for~commands}
+%<latexrelease>
+%    \end{macrocode}
+%    The command \cs{@@_cmd_begindocument_code:} is used in an
+%    internal hook, so we need to make sure it has a harmless
+%    definition after rollback as that will not remove it from the
+%    kernel hook.
+%    \begin{macrocode}
+%<latexrelease>\cs_set_eq:NN \@@_cmd_begindocument_code: \prg_do_nothing:
+%<latexrelease>
+%<latexrelease>\EndModuleRelease
+\ExplSyntaxOff
+%</2ekernel|latexrelease>
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%<@@=>
+%    \end{macrocode}
+%
+% \Finale
+%
diff --git a/Master/texmf-dist/source/latex-dev/base/ltdefns.dtx b/Master/texmf-dist/source/latex-dev/base/ltdefns.dtx
index ab9d4d0da16..7236083dfa2 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltdefns.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltdefns.dtx
@@ -32,7 +32,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltdefns.dtx}
-             [2021/01/15 v1.5o LaTeX Kernel (definition commands)]
+             [2021/04/19 v1.5o LaTeX Kernel (definition commands)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltdefns.dtx}
@@ -2419,7 +2419,8 @@
 %
 %
 % \begin{macro}{\g@addto@macro}
-% Globally add to the end of a macro.
+%    Globally add to the end of a macro.
+%    This macro is used by the kernel to add to its internal hooks.
 % \changes{v0.2a}{1993/11/14}{Made global}
 % \changes{v0.2w}{1994/01/31}
 %     {Use toks register to avoid `hash' problems}
diff --git a/Master/texmf-dist/source/latex-dev/base/ltexpl.dtx b/Master/texmf-dist/source/latex-dev/base/ltexpl.dtx
index a9be1b05211..6d7ec3ff60b 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltexpl.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltexpl.dtx
@@ -33,7 +33,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltexpl.dtx}
-             [2021/01/24 v1.3a LaTeX Kernel (expl3-dependent code)]
+             [2021/04/20 v1.3c LaTeX Kernel (expl3-dependent code)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltexpl.dtx}
@@ -82,21 +82,46 @@
 %    \begin{macrocode}
 %<*2ekernel|latexrelease>
 %<latexrelease>\IncludeInRelease{2020/10/01}%
-%<latexrelease>  {kernel@enddocument hooks}{Define kernel enddocument Hooks}%
-\let\@kernel@after@enddocument\@empty
-\let\@kernel@after@enddocument@afterlastpage\@empty
+%<latexrelease>  {kernel@enddocument hooks}{Define several kernel hooks}
+%    \end{macrocode}
+%    We only initialize these kernel hooks if they are not already
+%    existing. Otherwise they would be set to \cs{@empty} on rollback
+%    which would be wrong because code that has been added to to them
+%    may still have to be executed in the rollback situation . Instead
+%    code that writes to them needs to handle the rollback as needed.
+%    It is likely that we have to change that approach in the future,
+%    but for now it should do.
+%    (It is enough to test only for the existence of one hook, as all
+%    got added at the same time.)
+% \changes{v1.3c}{2021/04/20}{Don't empty kernel hooks on rollback}
+%    \begin{macrocode}
+\ifx\@kernel@after@enddocument\@undefined
+  \let \@kernel@after@enddocument               \@empty
+  \let \@kernel@after@enddocument@afterlastpage \@empty
+%    \end{macrocode}
+%
+%  \begin{macro}{\@kernel@before@begindocument,\@kernel@after@begindocument}
+%    For the similar reasons we also define those that are used in
+%    \cs{document} because they too get material added to in early modules.
+%    \begin{macrocode}
+  \let \@kernel@before@begindocument \@empty
+  \let \@kernel@after@begindocument  \@empty
+\fi
 %<latexrelease>\EndIncludeInRelease
 %    \end{macrocode}
 %
 %    \begin{macrocode}
 %<latexrelease>\IncludeInRelease{0000/00/00}%
-%<latexrelease>  {kernel@enddocument hooks}{Define kernel enddocument Hooks}%
+%<latexrelease>  {kernel@enddocument hooks}{Define several kernel hooks}
 %<latexrelease>\let\@kernel@after@enddocument\@undefined
 %<latexrelease>\let\@kernel@after@enddocument@afterlastpage\@undefined
-%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\let\@kernel@before@begindocument\@undefined
+%<latexrelease>\let\@kernel@after@begindocument\@undefined
 %</2ekernel|latexrelease>
+%<latexrelease>\EndIncludeInRelease
 %    \end{macrocode}
 % \end{macro}
+% \end{macro}
 %
 % First define some blank commands, so that in case something goes wrong while
 % loading \textsf{expl3}, we won't get strange \texttt{Undefined control
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfilehook.dtx b/Master/texmf-dist/source/latex-dev/base/ltfilehook.dtx
index 85c758ae608..e9309c41f78 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfilehook.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfilehook.dtx
@@ -31,8 +31,8 @@
 %%% From File: ltfilehook.dtx
 %
 %    \begin{macrocode}
-\providecommand\ltfilehookversion{v1.0g}
-\providecommand\ltfilehookdate{2021/02/08}
+\providecommand\ltfilehookversion{v1.0j}
+\providecommand\ltfilehookdate{2021/04/29}
 %    \end{macrocode}
 %
 %<*driver>
@@ -585,9 +585,13 @@
 %   places don't use \cs{InputIfFileExists} directly (\cs{include}) or
 %   need \cs{CurrentFile} earlier (\cs{@onefilewithoptions}), so these
 %   are manually used elsewhere as well.
+%   \changes{v1.0h}{2021/03/18}
+%           {Define \cs{g_@@_input_file_seq} to avoid losing data when
+%            rolling back.}
 %    \begin{macrocode}
 \tl_new:N \l_@@_internal_tl
-\seq_new:N \g_@@_input_file_seq
+\seq_if_exist:NF \g_@@_input_file_seq
+  { \seq_new:N \g_@@_input_file_seq }
 \cs_new_protected:Npn \@@_file_push:
   {
     \seq_gpush:Nx \g_@@_input_file_seq
@@ -601,7 +605,7 @@
     \seq_gpop:NNTF \g_@@_input_file_seq \l_@@_internal_tl
       { \exp_after:wN \@@_file_pop_assign:nnnn \l_@@_internal_tl }
       {
-        \msg_error:nnn { hooks } { should-not-happen }
+        \__kernel_msg_error:nnn { hooks } { should-not-happen }
           { Tried~to~pop~from~an~empty~file~name~stack. }
       }
   }
@@ -1031,15 +1035,18 @@
 %   false positives.  Here we define \cs{csname\cs{endcsname}} to
 %   expand to itself to avoid it matching the definition of some other
 %   control sequence.
+%   \changes{v1.0i}{2021/04/20}
+%           {Make \string~ expand to a string (tracks change in l3kernel)}
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>          {\set@curr@file}{Setting current file name}%
 \def\set@curr@file#1{%
   \begingroup
     \escapechar\m@ne
     \let\protect\string
+    \edef~{\string~}%
     \expandafter\def\csname\expandafter\endcsname
       \expandafter{\csname\endcsname}%
 %    \end{macrocode}
@@ -1078,6 +1085,7 @@
 %    
 %    \begin{macrocode}
 %<latexrelease>\IncludeInRelease{2020/10/01}%
+%<latexrelease>          {\set@curr@file}{Setting current file name}%
 %<latexrelease>\def\set@curr@file#1{%
 %<latexrelease>  \begingroup
 %<latexrelease>    \escapechar\m@ne
@@ -1529,7 +1537,7 @@
 %    
 %    \begin{macrocode}
 \cs_new_eq:NN \@expl@@@filehook@file@push@@
-               \__filehook_file_push:
+              \__filehook_file_push:
 %    \end{macrocode}
 %    
 %    \begin{macrocode}
@@ -1720,8 +1728,8 @@
 %    \Finale
 %
 %
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 \endinput
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %
 
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfiles.dtx b/Master/texmf-dist/source/latex-dev/base/ltfiles.dtx
index b27f9105873..bcaac582208 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfiles.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfiles.dtx
@@ -32,7 +32,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltfiles.dtx}
-             [2021/01/15 v1.2j LaTeX Kernel (File Handling)]
+             [2021/04/17 v1.2m LaTeX Kernel (File Handling)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltfiles.dtx}
@@ -195,19 +195,6 @@
 % \end{oldcomments}
 %
 %
-% \task{???}{Do we use @unused or mainaux?}
-%  \begin{macro}{\@inputcheck}
-%  \begin{macro}{\@unused}
-%    Allocate read stream for testing and output stream.
-% \changes{v1.0l}{1994/11/07}
-%      {move here from ltdefns, remove duplicate \cs{@mainaux}}
-%    \begin{macrocode}
-\newread\@inputcheck
-\newwrite\@unused
-%    \end{macrocode}
-%  \end{macro}
-%  \end{macro}
-%
 % \begin{macro}{\@mainaux}
 % \begin{macro}{\@partaux}
 %    \begin{macrocode}
@@ -470,9 +457,14 @@
 %    \end{macrocode}
 % \InternalDetectionOn
 %
+%    These internal hooks are already declared earlier (in
+%    \texttt{ltexpl}) so that other modules could write to them.
+% \changes{v1.2m}{2021/04/17}{Move \cs{@kernel@before@begindocument} and
+%  \cs{@kernel@after@begindocument} init earlier so that other modules can
+%    write to the hooks}
 %    \begin{macrocode}
-\let \@kernel@before@begindocument \@empty
-\let \@kernel@after@begindocument \@empty
+%\let \@kernel@before@begindocument \@empty
+%\let \@kernel@after@begindocument  \@empty
 %    \end{macrocode}
 %    
 %  \end{macro}
@@ -1072,30 +1064,114 @@
 %    \end{macrocode}
 %  \end{macro}
 %
+%    \begin{macrocode}
+%</2ekernel|latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{0000/00/00}%
+%<latexrelease>                 {\quote@name}{Quote file names}%
+%<latexrelease>
+%<latexrelease>\let\quote@name\@undefined
+%<latexrelease>\let\quote@@name\@undefined
+%<latexrelease>\let\unquote@name\@undefined
+%<latexrelease>
+%<latexrelease>\long\def \IfFileExists#1#2#3{%
+%<latexrelease>  \openin\@inputcheck#1 %
+%<latexrelease>  \ifeof\@inputcheck
+%<latexrelease>    \ifx\input@path\@undefined
+%<latexrelease>      \def\reserved@a{#3}%
+%<latexrelease>    \else
+%<latexrelease>      \def\reserved@a{\@iffileonpath{#1}{#2}{#3}}%
+%<latexrelease>    \fi
+%<latexrelease>  \else
+%<latexrelease>    \closein\@inputcheck
+%<latexrelease>    \edef\@filef@und{#1 }%
+%<latexrelease>    \def\reserved@a{#2}%
+%<latexrelease>  \fi
+%<latexrelease>  \reserved@a}
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<*2ekernel>
+%    \end{macrocode}
+%
+%
+%
 % \begin{macro}{\IfFileExists@}
 % \changes{v0.9b}{1993/12/04}{Macro added}
 % \changes{v0.9p}{1994/01/18}{New Definition}
 % \changes{v1.0t}{1995/05/25}{(CAR) added \cs{long}}
-% \changes{v1.2d}{2019/10/26}{quote on openin}%
+% \changes{v1.2d}{2019/10/26}{quote on openin}
+% \changes{v1.2k}{2021/03/12}{Allow unbalanced conditionals (gh/530)}
 % Argument |#1| is |\@curr@file| so catcode 12 string with no quotes.
+%
+%    The original definition picked up arguments |#2| and |#3| in a
+%    way that they couldn't contain unbalanced conditionals. A better
+%    implementation would have been not to pick up the arguments at
+%    all but instead use the usual \cs{@firstoftwo} and
+%    \cs{secondoftwo}. However, that changes how |#| is interpreted
+%    and so we can't do that nowaways without invalidating a lot of
+%    code. Therefore the somewhat curious construction near the end.
 %    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>                 {\IfFileExists@}{manage unbalanced conditionals}
 \long\def \IfFileExists@#1#2#3{%
   \openin\@inputcheck"#1" %
   \ifeof\@inputcheck
     \ifx\input@path\@undefined
-      \def\reserved@a{#3}%
+      \let\reserved@a\@secondoftwo
     \else
-      \def\reserved@a{\@iffileonpath{#1}{#2}{#3}}%
+      \def\reserved@a{\@iffileonpath{#1}}%
     \fi
   \else
     \closein\@inputcheck
     \edef\@filef@und{"#1" }%
-    \def\reserved@a{#2}%
+    \let\reserved@a\@firstoftwo
   \fi
-  \reserved@a}
+%    \end{macrocode}
+%    This is just there so that any |#| inside |#2| or |#3| needs
+%    doubling (as that was the case in the past).
+%    \begin{macrocode}
+  \expandafter\def\expandafter\reserved@a
+    \expandafter{\reserved@a{#2}{#3}}%
+\reserved@a}
+%</2ekernel|latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{2019/10/01}%
+%<latexrelease>                 {\IfFileExists@}{manage unbalanced conditionals}
+%<latexrelease>
+%<latexrelease>\long\def \IfFileExists@#1#2#3{%
+%<latexrelease>  \openin\@inputcheck"#1" %
+%<latexrelease>  \ifeof\@inputcheck
+%<latexrelease>    \ifx\input@path\@undefined
+%<latexrelease>      \def\reserved@a{#3}%
+%<latexrelease>    \else
+%<latexrelease>      \def\reserved@a{\@iffileonpath{#1}{#2}{#3}}%
+%<latexrelease>    \fi
+%<latexrelease>  \else
+%<latexrelease>    \closein\@inputcheck
+%<latexrelease>    \edef\@filef@und{"#1" }%
+%<latexrelease>    \def\reserved@a{#2}%
+%<latexrelease>  \fi
+%<latexrelease>  \reserved@a}
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{0000/00/00}%
+%<latexrelease>                 {\IfFileExists@}{manage unbalanced conditionals}
+%<latexrelease>
+%<latexrelease>\let\IfFileExists@\@undefined
+%<latexrelease>
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<*2ekernel>
 %    \end{macrocode}
 %  \end{macro}
 %
+%
+%
+%
+%
+%
+%
 % \begin{macro}{\@iffileonpath}
 % If the file is not found by |\openin|, and |\input@path| is defined,
 % look in all the directories specified in |\input@path|.
@@ -1109,6 +1185,10 @@
 % \changes{v1.2d}{2019/10/26}{quote on openin}%
 % \changes{v1.2f}{2019/11/11}{make \cs{@filef@und} match quoting used on \cs{openin}}%
 %    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2019/10/01}%
+%<latexrelease>                 {\@iffileonpath}{Quote file names}
 \long\def\@iffileonpath#1{%
   \let\reserved@a\@secondoftwo
   \expandafter\@tfor\expandafter\reserved@b\expandafter
@@ -1128,28 +1208,7 @@
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
 %<latexrelease>\IncludeInRelease{0000/00/00}%
-%<latexrelease>                 {\quote@name}{Quote file names}%
-%<latexrelease>
-%<latexrelease>\let\quote@name\@undefined
-%<latexrelease>\let\quote@@name\@undefined
-%<latexrelease>\let\unquote@name\@undefined
-%<latexrelease>
-%<latexrelease>\let\IfFileExists@\@undefined
-%<latexrelease>
-%<latexrelease>\long\def \IfFileExists#1#2#3{%
-%<latexrelease>  \openin\@inputcheck#1 %
-%<latexrelease>  \ifeof\@inputcheck
-%<latexrelease>    \ifx\input@path\@undefined
-%<latexrelease>      \def\reserved@a{#3}%
-%<latexrelease>    \else
-%<latexrelease>      \def\reserved@a{\@iffileonpath{#1}{#2}{#3}}%
-%<latexrelease>    \fi
-%<latexrelease>  \else
-%<latexrelease>    \closein\@inputcheck
-%<latexrelease>    \edef\@filef@und{#1 }%
-%<latexrelease>    \def\reserved@a{#2}%
-%<latexrelease>  \fi
-%<latexrelease>  \reserved@a}
+%<latexrelease>                 {\quote@name}{Quote file names}
 %<latexrelease>
 %<latexrelease>\long\def\@iffileonpath#1{%
 %<latexrelease>  \let\reserved@a\@secondoftwo
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfinal.dtx b/Master/texmf-dist/source/latex-dev/base/ltfinal.dtx
index d6fa6e8a7bf..19f82934aa6 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfinal.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfinal.dtx
@@ -33,7 +33,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltfinal.dtx}
-             [2021/02/25 v2.2m LaTeX Kernel (Final Settings)]
+             [2021/04/18 v2.2o LaTeX Kernel (Final Settings)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltfinal.dtx}
@@ -242,7 +242,73 @@
 % \end{macro}
 % \end{macro}
 %
-%
+% \begin{macro}{trace_stack_levels}
+%   Now define the Lua function to emulate \cs{tracingstacklevels} and
+%   install it in the \texttt{input_level_string} callback.
+%    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%    \end{macrocode}
+%   In \texttt{latexrelease} mode we always remove the function from
+%   the callback, then add the correct version later.
+%    \begin{macrocode}
+%<latexrelease>\ifx\directlua\@undefined
+%<latexrelease>\else
+%<latexrelease>  \directlua{%
+%<latexrelease>    if luatexbase.callbacktypes['input_level_string'] and %
+%<latexrelease>       luatexbase.in_callback('input_level_string','tracingstacklevels') then
+%<latexrelease>        luatexbase.remove_from_callback('input_level_string','tracingstacklevels')
+%<latexrelease>    end}%
+%<latexrelease>\fi
+%<latexrelease>\IncludeInRelease{2021/06/01}{trace_stack_levels}%
+%<latexrelease>                 {Lua trace_stack_levels function}%
+\ifx\directlua\@undefined
+\else
+%<*2ekernel>
+  \expanded{%
+    \everyjob{\the\everyjob
+    \noexpand%\directlua
+%</2ekernel>
+    \directlua{%
+      local function trace_stack_levels (input_ptr)
+        local tracingstacklevels = tex.count.tracingstacklevels
+        if tex.tracingmacros > 0 or input_ptr < tracingstacklevels then
+          if tracingstacklevels > 0 then
+            if input_ptr < tracingstacklevels then
+              return "\string\n\string~" .. string.rep(".",input_ptr)
+            else
+              return "\string~\string~"
+            end
+          else
+            return "\string\n"
+          end
+        else
+          return ""
+        end
+      end
+%<latexrelease>    if luatexbase.callbacktypes['input_level_string'] then
+      luatexbase.add_to_callback('input_level_string',
+        trace_stack_levels,'tracingstacklevels')
+%<latexrelease>    end
+    }%
+%<*2ekernel>
+  }}%
+%</2ekernel>
+\fi
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>
+%    \end{macrocode}
+%   Then for the full rollback, just do nothing, since the function
+%   was already taken out of the rollback above.
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{0000/00/00}{trace_stack_levels}%
+%<latexrelease>                 {Lua trace_stack_levels function}%
+%<latexrelease>% Nothing here
+%<latexrelease>\EndIncludeInRelease
+%</2ekernel|latexrelease>
+%<*2ekernel>
+%    \end{macrocode}
+% \end{macro}
 %
 % The default values of the picture and |\fbox| parameters:
 %    \begin{macrocode}
@@ -574,7 +640,7 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\pdfgentounicode}{Preload glyphtounicode}%
 \ifx \pdfgentounicode \@undefined \else
 %<*2ekernel>
@@ -1194,7 +1260,6 @@
 %         {Load first aid file if existing}
 %    \begin{macrocode}
 \@input{latex2e-first-aid-for-external-files.ltx}
-\@input{ltpara.ltx}
 %    \end{macrocode}
 %
 %
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfloat.dtx b/Master/texmf-dist/source/latex-dev/base/ltfloat.dtx
index f2324118a04..ed25db3ed10 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfloat.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfloat.dtx
@@ -31,7 +31,7 @@
 %
 %<*driver>
 % \fi
-\ProvidesFile{ltfloat.dtx}[2021/02/10 v1.2f LaTeX Kernel (Floats)]
+\ProvidesFile{ltfloat.dtx}[2021/03/03 v1.2f LaTeX Kernel (Floats)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltfloat.dtx}
@@ -1008,7 +1008,7 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\@savemarbox}{Explicit par for marginpar}%
 \long\def \@savemarbox #1#2{%
   \global\setbox #1%
@@ -1513,7 +1513,7 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\@footnotetext}{footnotetext tagging}%
 \long\def\@footnotetext#1{\insert\footins{%
     \reset@font\footnotesize
@@ -1633,7 +1633,7 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\footref}{Add footref}%
 \def\footref#1{%
   \begingroup
@@ -1644,14 +1644,16 @@
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
 %    \end{macrocode}
-%    We don't remove it when rolling back.
+%    We don't remove it when rolling back so that packages offered it
+%    in the past do not need to alter their behavior in a rollback
+%    situation.
 %    \begin{macrocode}
-%%<latexrelease>\IncludeInRelease{0000/00/00}%
-%%<latexrelease>                 {\footref}{Add footref}%
-%%<latexrelease>
-%%<latexrelease>\let\footref\@undefined
-%%<latexrelease>
-%%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{0000/00/00}%
+%<latexrelease>                 {\footref}{Add footref}%
+%<latexrelease>
+%<latexrelease>  % \let\footref\@undefined
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
 %<*2ekernel>
 %    \end{macrocode}
 %  \end{macro}
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfssaxes.dtx b/Master/texmf-dist/source/latex-dev/base/ltfssaxes.dtx
index e0c07874556..86c84b111fb 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfssaxes.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfssaxes.dtx
@@ -35,7 +35,7 @@
 %
 %
 \ProvidesFile{ltfssaxes.dtx}
-             [2021/01/15 v1.0h LaTeX Kernel (NFSS Axes handing)]
+             [2021/03/18 v1.0i LaTeX Kernel (NFSS Axes handing)]
 % \iffalse
 \documentclass{ltxdoc}
 \begin{document}
@@ -699,7 +699,7 @@
 %
 %    \begin{macrocode}
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\fontseries}{delay fontseries update}%
 %    \end{macrocode}
 %
@@ -772,11 +772,12 @@
 %<latexrelease>
 %    \end{macrocode}
 %    For a roll forward we may have to define \cs{if@forced@series}
-%    but this needs doing in a somewhat roundabout way.
+%    but this needs doing in a way that \TeX{} doesn't see it when
+%    skipping over conditionals.
+% \changes{v1.0i}{2021/03/18}
+%         {Fix rollforward definition.}
 %    \begin{macrocode}
-%<latexrelease>\ifx\@forced@seriestrue\@undefined \else
-%<latexrelease>  \expandafter\newif\csname if@forced@series\endcsname
-%<latexrelease>\fi
+%<latexrelease>\expandafter\newif\csname if@forced@series\endcsname
 %<latexrelease>
 %<latexrelease>\EndIncludeInRelease
 %    \end{macrocode}
@@ -1328,7 +1329,7 @@
 %
 %    \begin{macrocode}
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>   {\fontshape}{Font shape change}%
 %    \end{macrocode}
 %
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfssbas.dtx b/Master/texmf-dist/source/latex-dev/base/ltfssbas.dtx
index 6d575fc9d0b..df265d0b0fc 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfssbas.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfssbas.dtx
@@ -35,7 +35,7 @@
 %
 %
 \ProvidesFile{ltfssbas.dtx}
-             [2020/12/10 v3.2h LaTeX Kernel (NFSS Basic Macros)]
+             [2021/04/26 v3.2i LaTeX Kernel (NFSS Basic Macros)]
 % \iffalse
 \documentclass{ltxdoc}
 \begin{document}
@@ -896,15 +896,35 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2020/02/02}%
-%<latexrelease>                 {\usefont}{Drop m in usefont}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>                 {\usefont}{Force font face}%
 \DeclareRobustCommand\usefont[4]{\fontencoding{#1}%
    \edef\f@family{#2}%
    \set@target@series{#3}%
-   \edef\f@shape{#4}\selectfont
+   \edef\f@shape{#4}%
+%    \end{macrocode}
+%    Any earlier \cs{fontseries}, etc.\ should be canceled and we
+%    should switch unconditionally to the requested font face so we
+%    drop any  code that may have been stored in
+%    \cs{delayed@f@adjustment}.
+% \changes{v3.2i}{2021/04/26}{Unconditionally switch to the requested
+%    font face (gh/444)}
+%    \begin{macrocode}
+   \let\delayed@f@adjustment\@empty
+   \selectfont
    \ignorespaces}
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{2020/02/02}%
+%<latexrelease>                 {\usefont}{Drop m in usefont}%
+%<latexrelease>
+%<latexrelease>\DeclareRobustCommand\usefont[4]{\fontencoding{#1}%
+%<latexrelease>   \edef\f@family{#2}%
+%<latexrelease>   \set@target@series{#3}%
+%<latexrelease>   \edef\f@shape{#4}\selectfont
+%<latexrelease>   \ignorespaces}
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
 %<latexrelease>\IncludeInRelease{0000/00/00}%
 %<latexrelease>                 {\usefont}{Drop m in usefont}%
 %<latexrelease>
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfssini.dtx b/Master/texmf-dist/source/latex-dev/base/ltfssini.dtx
index 361adac9c36..b06fc161b08 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfssini.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfssini.dtx
@@ -36,7 +36,7 @@
 %
 %
 \ProvidesFile{ltfssini.dtx}
-             [2021/01/15 v3.2f LaTeX Kernel (NFSS Initialisation)]
+             [2021/04/26 v3.2h LaTeX Kernel (NFSS Initialisation)]
 % \iffalse
 \documentclass{ltxdoc}
 \begin{document}
@@ -1088,6 +1088,8 @@
 %  \end{macro}
 %
 %
+% \changes{v3.2g}{2021/03/18}
+%         {Add legacy hook definitions for rollback.}
 %    \begin{macrocode}
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
@@ -1140,6 +1142,9 @@
 %<latexrelease>   \prepare@family@series@update{tt}\ttdefault
 %<latexrelease>   \@ttfamilyhook
 %<latexrelease>   \selectfont}
+%<latexrelease>\let\@rmfamilyhook\@empty
+%<latexrelease>\let\@sffamilyhook\@empty
+%<latexrelease>\let\@ttfamilyhook\@empty
 %<latexrelease>
 %    \end{macrocode}
 %    
@@ -1765,7 +1770,7 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2020/02/02}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\normalfont}{Add hook to \normalfont}%
 \DeclareRobustCommand\normalfont{%
 %    \end{macrocode}
@@ -1778,6 +1783,15 @@
    \edef\f@series{\seriesdefault}%
    \edef\f@shape{\shapedefault}%
 %    \end{macrocode}
+%    Any earlier \cs{fontseries}, etc.\ should be canceled and we
+%    should switch unconditionally to the requested font face so we
+%    drop any  code that may have been stored in
+%    \cs{delayed@f@adjustment}.
+% \changes{v3.2h}{2021/04/26}{Unconditionally switch to the requested
+%    font face (gh/444)}
+%    \begin{macrocode}
+   \let\delayed@f@adjustment\@empty
+%    \end{macrocode}
 %    
 % \changes{v3.2b}{2020/08/21}{Integration of new hook management interface}
 %    \begin{macrocode}
@@ -1789,18 +1803,54 @@
    \@defaultfamilyhook        % hookname from 2020/02 will vanish
    \selectfont}
 %    \end{macrocode}
-%    
+%
 %    \begin{macrocode}
 \let\reset@font\normalfont
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
-%    
+%
 %
 %
 %    \begin{macrocode}
+% \changes{v3.2g}{2021/03/18}
+%         {Add missing 2020/02/02 latexrelease entry.}
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
+%<latexrelease>
+%<latexrelease>\IncludeInRelease{2020/10/01}%
+%<latexrelease>                 {\normalfont}{Add hook to \normalfont}%
+%<latexrelease>
+%<latexrelease>\DeclareRobustCommand\normalfont{%
+%<latexrelease>   \fontencoding\encodingdefault
+%<latexrelease>   \edef\f@family{\familydefault}%
+%<latexrelease>   \edef\f@series{\seriesdefault}%
+%<latexrelease>   \edef\f@shape{\shapedefault}%
+%<latexrelease>   \UseHook{normalfont}%
+%<latexrelease>   \@defaultfamilyhook        % hookname from 2020/02 will vanish
+%<latexrelease>   \selectfont}
+%<latexrelease>
+%<latexrelease>\let\reset@font\normalfont
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>
+%<latexrelease>\IncludeInRelease{2020/02/02}%
+%<latexrelease>                 {\normalfont}{Add hook to \normalfont}%
+%<latexrelease>
+%<latexrelease>\DeclareRobustCommand\normalfont{%
+%<latexrelease>   \fontencoding\encodingdefault
+%<latexrelease>   \edef\f@family{\familydefault}%
+%<latexrelease>   \edef\f@series{\seriesdefault}%
+%<latexrelease>   \edef\f@shape{\shapedefault}%
+%<latexrelease>   \@defaultfamilyhook
+%<latexrelease>   \selectfont}
+%<latexrelease>
+%<latexrelease>\let\reset@font\normalfont
+%<latexrelease>
+%<latexrelease>\let\@defaultfamilyhook\@empty
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>
 %<latexrelease>\IncludeInRelease{0000/00/00}%
 %<latexrelease>                 {\normalfont}{Add hook to \normalfont}%
 %<latexrelease>
diff --git a/Master/texmf-dist/source/latex-dev/base/ltfsstrc.dtx b/Master/texmf-dist/source/latex-dev/base/ltfsstrc.dtx
index 961abafc8a3..c6aec105ba5 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltfsstrc.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltfsstrc.dtx
@@ -32,12 +32,12 @@
 %% Copyright (C) 1989-97 by Frank Mittelbach and Rainer Sch\"opf.
 %% Copyright (C) 1994-97 by LaTeX Project. All rights reserved.
 %
-%<package>\NeedsTeXFormat{LaTeX2e}[2021/05/01]
+%<package>\NeedsTeXFormat{LaTeX2e}[2021/06/01]
 %<package>\ProvidesPackage{tracefnt}
 %<package>     [2020/12/22 v3.0n  Standard LaTeX package (font tracing)]
 % \fi
 % \ProvidesFile{ltfsstrc.dtx}
-%              [2020/12/22 v3.0n LaTeX Kernel (NFSS tracing)]
+%              [2021/04/26 v3.0o LaTeX Kernel (NFSS tracing)]
 %
 % \iffalse
 %<+checkmem>\CHECKMEM
@@ -423,7 +423,7 @@
 
 %    \begin{macrocode}
 %<*2ekernel|latexrelease|package>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\selectfont}{Add hook to \selectfont}%
 %    \end{macrocode}
 %
@@ -525,6 +525,14 @@
       \let\delayed@f@adjustment\@empty
     \fi
 %    \end{macrocode}
+%    If the series was forced we should now cancel that in case the
+%    next series change is done with some low-level setting to
+%    \cs{f@series}.
+% \changes{v3.0o}{2021/04/26}{Unset the forced series boolean when reaching
+%    \cs{selectfont} (gh/444)}
+%    \begin{macrocode}
+    \@forced@seriesfalse
+%    \end{macrocode}
 %    Then we generate the internal name of the font
 %    by concatenating {\em family}, {\em series},
 %    {\em shape}, and current {\em size},
@@ -610,7 +618,7 @@
 %    package to support rollback. In packages that works a bit
 %    differently and therefore we have to provide an empty block there.   
 %    \begin{macrocode}
-%<package>\IncludeInRelease{2021/05/01}%
+%<package>\IncludeInRelease{2021/06/01}%
 %<package>                 {\selectfont}{Add hook to \selectfont}%
 %<package>\EndIncludeInRelease
 %    \end{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/base/lthooks.dtx b/Master/texmf-dist/source/latex-dev/base/lthooks.dtx
index 803914b4a74..45d6a78aba1 100644
--- a/Master/texmf-dist/source/latex-dev/base/lthooks.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/lthooks.dtx
@@ -31,8 +31,8 @@
 %%% From File: lthooks.dtx
 %
 %    \begin{macrocode}
-\def\lthooksversion{v1.0h}
-\def\lthooksdate{2021/01/15}
+\def\lthooksversion{v1.0m}
+\def\lthooksdate{2021/04/29}
 %    \end{macrocode}
 %
 %<*driver>
@@ -67,10 +67,13 @@
 % \fi
 %
 %
-% \long\def\fmi#1{\begin{quote}\itshape FMi: #1\end{quote}}
-% \long\def\pho#1{\begin{quote}\itshape PhO: #1\end{quote}}
+% \providecommand\hook[1]{\texttt{#1}}
+%
+% \providecommand\fmi[1]{\marginpar{\footnotesize FMi: #1}}
+% \providecommand\fmiinline[1]{\begin{quote}\itshape\footnotesize FMi: #1\end{quote}}
+% \providecommand\pho[1]{\marginpar{\footnotesize PhO: #1}}
+% \providecommand\phoinline[1]{\begin{quote}\itshape\footnotesize PhO: #1\end{quote}}
 %
-% \newcommand\hook[1]{\texttt{#1}}
 %    
 %
 % \title{The \texttt{lthooks} package\thanks{This package has version
@@ -122,14 +125,15 @@
 %
 % \subsection{\LaTeXe\ interfaces}
 %
-% \subsubsection{Declaring hooks and using them in code}
+% \subsubsection{Declaring hooks}
 %
-%    With two exceptions, hooks have to be declared before they can be
-%    used. The exceptions are hooks in environments (i.e., executed at
-%    \cs{begin} and \cs{end}) and hooks run when loading files,
-%    e.g. before and after a package is loaded, etc. Their hook names
-%    depend on the environment or the file name and so declaring them
-%    beforehand is difficult.
+%    With a few exceptions, hooks have to be declared before they can
+%    be used. The exceptions are the generic hooks for commands,
+%    environments (i.e., executed at \cs{begin} and \cs{end}) and
+%    hooks run when loading files, e.g. before and after a package is
+%    loaded, etc. Their hook names depend on the command,
+%    environment or the
+%    file name and so declaring them beforehand is not practical.
 %
 %
 % \begin{function}{\NewHook}
@@ -176,6 +180,62 @@
 % \end{function}
 %
 %
+% \subsubsection{Special declarations for hooks}
+%
+%    The declarations here should normally not be used. They are available
+%    to provide support for special use cases mainly involving
+%    generic command hooks.
+%
+% \begin{function}{\DisableHook}
+%   \begin{syntax}
+%     \cs{DisableHook} \Arg{hook}
+%   \end{syntax}
+%    After this declaration the \meta{hook} is no longer usable: Any
+%    attempt to add further code to it will result in an error and any
+%    use, e.g., via \cs{UseHook}, will simply do nothing.
+%
+%    This is intended to be used with generic command hooks (see
+%    \texttt{ltcmdhooks-doc}) as depending on the definition of the
+%    command such generic hooks may be unusable. If that is known, a
+%    package developer can disable such hooks up front.
+%
+%    The \meta{hook} can be specified using the dot-syntax to denote
+%    the current package name. See section~\ref{sec:default-label}.
+% \end{function}
+%
+%
+% \begin{function}{\ProvideHook}
+%   \begin{syntax}
+%     \cs{ProvideHook} \Arg{hook}
+%   \end{syntax}
+%   Like \cs{NewHook} but does nothing if the hook was previously
+%    declared with \cs{NewHook}.  This declaration should only be used
+%    in special situations, e.g., when  command of another package
+%    need to be altered and it is is not clear if for that command a
+%    generic hook was already explicitly declared before.
+%
+%    Normally \cs{NewHook} should be used instead.
+% \end{function}
+%
+% \begin{function}{\ProvideReversedHook}
+%   \begin{syntax}
+%     \cs{ProvideReversedHook} \Arg{hook}
+%   \end{syntax}
+%   Like \cs{NewReversedHook} but does nothing if the hook was
+%    previously declared as a reversed hook.
+% \end{function}
+%
+% \begin{function}{\ProvideMirroredHookPair}
+%   \begin{syntax}
+%     \cs{ProvideMirroredHookPair} \Arg{hook-1} \Arg{hook-2}
+%   \end{syntax}
+%     A shorthand for
+%    \cs{ProvideHook}\Arg{hook-1}\cs{ProvideReversedHook}\Arg{hook-2}.
+% \end{function}
+%
+%
+%
+% \subsubsection{Using hooks in code}
 %
 %
 % \begin{function}{\UseHook}
@@ -201,7 +261,7 @@
 %    Some hooks are only used (and can be only used) in one place, for
 %    example, those in \verb=\begin{document}= or
 %    \verb=\end{document}=. Once we have passed that point adding to
-%    the hook through a defined \cs{\meta{addto-cmd}} command (e.g.,
+%    the hook through a defined \cs[no-index]{\meta{addto-cmd}} command (e.g.,
 %    \cs{AddToHook} or \cs{AtBeginDocument}, etc.\@) would have no
 %    effect (as would the use of such a command inside the hook code
 %    itself). It is therefore customary to redefine
@@ -212,10 +272,12 @@
 %    consumed and any further attempt to add to it will result in
 %    executing the code to be added immediately.
 %
-%    \fmi{Maybe add an error version as well?}
+%    \fmiinline{Maybe add an error version as well?}
 %
 %    The \meta{hook} \emph{cannot} be specified using the dot-syntax.
-%    A leading |.| is treated literally.
+%    A leading |.| is treated literally.    See
+%    section~\ref{sec:default-label} for details.
+
 % \end{function}
 %
 %
@@ -264,9 +326,10 @@
 %    that label, the removal order takes action and the code is not
 %    added.
 %
-%    If the optional argument is \texttt{*}, then all code chunks are
+%    If the optional \meta{label} argument is \texttt{*}, then all code chunks are
 %    removed. This is rather dangerous as it drops code from other
-%    packages one may not know about!
+%    packages one may not know about and should therefore not by used
+%    by packages but only in document preambles!
 %
 %    The \meta{hook} and \meta{label} can be specified using the
 %    dot-syntax to denote the current package name.
@@ -299,7 +362,7 @@
 %\end{verbatim}
 % because that only \enquote{adds} a further empty chunk of code to
 % the hook. Adding \cs{normalsize} would work but that means the hook
-% then contained \cs{small}\cs{normalsize} which means to font size
+% then contained \cs{small}\cs{normalsize} which means two font size
 % changes for no good reason.
 %
 % The above is only needed if one wants to typeset several quotes in a
@@ -359,10 +422,9 @@
 % \meta{label} throughout the sub-packages in order to avoid
 % that the labels change if you internally reorganize your code.
 %
-% Except for \cs{UseHook}, \cs{UseOneTimeHook}, \cs{IfHookEmptyTF}, and
-% \cs{IfHookExistsTF} (and their \pkg{expl3} interfaces \cs{hook_use:n},
-% \cs{hook_use_once:n}, \cs{hook_if_empty:nTF}, and
-% \cs{hook_if_exist:nTF}), all \meta{hook}
+% Except for \cs{UseHook}, \cs{UseOneTimeHook} and \cs{IfHookEmptyTF}
+% (and their \pkg{expl3} interfaces \cs{hook_use:n},
+% \cs{hook_use_once:n} and \cs{hook_if_empty:nTF}, all \meta{hook}
 % and \meta{label} arguments are processed in the same way: first,
 % spaces are trimmed around the argument, then it is fully expanded
 % until only character tokens remain.  If the full expansion of the
@@ -370,8 +432,8 @@
 % token, a low-level \TeX{} error is raised (namely, the \meta{hook} is
 % expanded using \TeX's \cs{csname}\ldots\cs{endcsname}, as such,
 % Unicode characters are allowed in \meta{hook} and \meta{label}
-% arguments).  The arguments of \cs{UseHook}, \cs{UseOneTimeHook},
-% \cs{IfHookEmptyTF}, and \cs{IfHookExistsTF} are
+% arguments).  The arguments of \cs{UseHook}, \cs{UseOneTimeHook}, and
+% \cs{IfHookEmptyTF} are
 % processed much in the same way except that spaces are not trimmed
 % around the argument, for better performance.
 %
@@ -425,8 +487,7 @@
 % this syntax is not available in \cs{UseHook} (and \cs{hook_use:n})
 % because the hook is most of the time used outside of the package file
 % in which it was defined. This syntax is also not available in the hook
-% conditionals \cs{IfHookEmptyTF} (and \cs{hook_if_empty:nTF}) and
-% \cs{IfHookExistsTF} (and \cs{hook_if_exist:nTF}) because these
+% conditionals \cs{IfHookEmptyTF} (and \cs{hook_if_empty:nTF}), because these
 % conditionals are used in some performance-critical parts of the hook
 % management code, and because they are usually used to refer to other
 % package's hooks, so the dot-syntax doesn't make much sense.
@@ -435,7 +496,7 @@
 % it in logical parts, but still use the main package name as
 % \meta{label}, then the \meta{default label} can be set using
 % \cs{SetDefaultHookLabel} or
-% \cs{PushDefaultHookLabel}..\cs{PopDefaultHookLabel}.
+% \cs{PushDefaultHookLabel}\verb={..}=\,\ldots\cs{PopDefaultHookLabel}.
 %
 % \begin{function}{\PushDefaultHookLabel,\PopDefaultHookLabel}
 %   \begin{syntax}
@@ -651,9 +712,10 @@
 %   \item exist and be non-empty; and
 %   \item not exist (in which case emptiness doesn't apply);
 % \end{itemize}
-% Hooks are a bit more complicated: they have four possible states.
-% A hook may exist or not, and either way it may or may not be empty.
-% This means that even a hook that doesn't exist may be non-empty.
+% Hooks are a bit more complicated: 
+% a hook may exist or not, and either way it may or may not be empty.
+% This means that even a hook that doesn't exist may be non-empty and
+%    it can also be disabled.
 %
 % This seemingly strange state may happen when, for example, package~$A$
 % defines hook \hook{A/foo}, and package $B$ adds some code to that
@@ -664,11 +726,17 @@
 % querying the existence of a hook doesn't imply its emptiness, neither
 % does the other way around.
 %
+% Given that code or rules can be added to a hook even if it doesn't
+% physically exist yet, means that a querying its existence has no
+% real use case (in contrast to other variables that can only be
+% update if they have already been declared). For that reason only the
+% test for emptiness has a public interface.
+%
 % A hook is said to be empty when no code was added to it, either to
 % its permanent code pool, or to its ``next'' token list.  The hook
 % doesn't need to be declared to have code added to its code pool.
 % A hook is said to exist when it was declared with \cs{NewHook} or
-% some variant thereof.  Generic \hook{file} and \hook{env} hooks are
+% some variant thereof.  Generic hooks such as \hook{file} and \hook{env} hooks are
 % automatically declared when code is added to them.
 %
 % \begin{function}[EXP]{\IfHookEmptyTF}
@@ -676,7 +744,8 @@
 %     \cs{IfHookEmptyTF} \Arg{hook} \Arg{true code} \Arg{false code}
 %   \end{syntax}
 %   Tests if the \meta{hook} is empty (\emph{i.e.}, no code was added to
-%   it using either \cs{AddToHook} or \cs{AddToHookNext}), and
+%   it using either \cs{AddToHook} or \cs{AddToHookNext}) or such code
+%    was removed again (via \cs{RemoveFromHook}), and
 %   branches to either \meta{true code} or \meta{false code} depending
 %   on the result.
 %
@@ -684,30 +753,7 @@
 %    A leading |.| is treated literally.
 % \end{function}
 %
-% \begin{function}[EXP]{\IfHookExistsTF}
-%   \begin{syntax}
-%     \cs{IfHookExistsTF} \Arg{hook} \Arg{true code} \Arg{false code}
-%   \end{syntax}
-%   Tests if the \meta{hook} exists (if it was created with either
-%   \cs{NewHook}, \cs{NewReversedHook}, or \cs{NewMirroredHookPair}), and
-%   branches to either \meta{true code} or \meta{false code} depending
-%   on the result.
-%
-%   The existence of a hook usually doesn't mean much from the viewpoint
-%   of code that tries to add/remove code from that hook, since package
-%   loading order may vary, thus the creation of hooks is asynchronous
-%   to adding and removing code from it, so this test should be used
-%   sparingly.
-%
-%   Generic hooks are declared at the time code is added to them, so the
-%   result of \cs{hook_if_exist:n} will change once code is added to
-%   said hook (unless the hook was previously declared).
 %
-%    The \meta{hook} \emph{cannot} be specified using the dot-syntax.
-%    A leading |.| is treated literally.
-% \end{function}
-%
-% \fmi{Would be helpful if we provide some use cases}
 %
 % \subsubsection{Displaying hook code}
 %
@@ -822,7 +868,7 @@
 %   \begin{syntax}
 %     \cs{DebugHooksOn}
 %   \end{syntax}
-%    Turn the debugging of hook code on or off. This displays changes
+%    Turn the debugging of hook code on or off. This displays most changes
 %    made to the hook data structures. The output is rather coarse and
 %      not really intended for normal use.
 % \end{function}
@@ -859,6 +905,53 @@
 %
 %
 %
+% \begin{function}{\hook_disable:n}
+%   \begin{syntax}
+%     \cs{hook_disable:n} \Arg{hook}
+%   \end{syntax}
+%    Marks \Arg{hook} as disabled. Any further attempt to add code to
+%    it or declare it, will result in an error and any call to
+%    \cs{hook_use:n} will simply do nothing.
+%
+%    This declaration is intended for use with generic hooks that are
+%    known not to work (see \texttt{ltcmdhooks-doc}) if they receive
+%    code.
+%
+%    The \meta{hook} can be specified using the dot-syntax to denote
+%    the current package name. See section~\ref{sec:default-label}.
+% \end{function}
+%
+% \begin{function}{\hook_provide:n}
+%   \begin{syntax}
+%     \cs{hook_provide:n} \Arg{hook}
+%   \end{syntax}
+%    Like \cs{hook_new:n} but does nothing if the hook was previously
+%    declared with \cs{hook_new:n}.  This declaration should only be used
+%    in special situations, e.g., when a command of another package
+%    needs to be altered and it is is not clear if for that command a
+%    generic \hook{cmd} hook was already explicitly declared before.
+%
+%    Normally \cs{hook_new:n} should be used instead.
+% \end{function}
+%
+% \begin{function}{\hook_provide_reversed:n}
+%   \begin{syntax}
+%     \cs{hook_provide_reversed:n} \Arg{hook}
+%   \end{syntax}
+%   Like \cs{hook_new_reversed:n} but does nothing if the hook was
+%    previously declared as a reversed hook.
+% \end{function}
+%
+% \begin{function}{\hook_provide_pair:nn}
+%   \begin{syntax}
+%     \cs{hook_provide_pair:nn} \Arg{hook-1} \Arg{hook-2}
+%   \end{syntax}
+%     A shorthand for
+%    \cs{hook_provide:n}\Arg{hook-1}\cs{hook_provide_reversed:n}\Arg{hook-2}.
+% \end{function}
+%
+%
+%
 % \begin{function}{\hook_use:n}
 %   \begin{syntax}
 %     \cs{hook_use:n} \Arg{hook}
@@ -971,28 +1064,6 @@
 %    A leading |.| is treated literally.
 % \end{function}
 %
-% \begin{function}[pTF]{\hook_if_exist:n}
-%   \begin{syntax}
-%     \cs{hook_if_exist:nTF} \Arg{hook} \Arg{true code} \Arg{false code}
-%   \end{syntax}
-%   Tests if the \meta{hook} exists (if it was created with either
-%   \cs{NewHook}, \cs{NewReversedHook}, or \cs{NewMirroredHookPair}), and
-%   branches to either \meta{true code} or \meta{false code} depending
-%   on the result.
-%
-%   The existence of a hook usually doesn't mean much from the viewpoint
-%   of code that tries to add/remove code from that hook, since package
-%   loading order may vary, thus the creation of hooks is asynchronous
-%   to adding and removing code from it, so this test should be used
-%   sparingly.
-%
-%   Generic hooks are declared at the time code is added to them, so the
-%   result of \cs{hook_if_exist:n} will change once code is added to
-%   said hook (unless the hook was previously declared).
-%
-%    The \meta{hook} \emph{cannot} be specified using the dot-syntax.
-%    A leading |.| is treated literally.
-% \end{function}
 %
 % \begin{function}{\hook_show:n,\hook_log:n}
 %   \begin{syntax}
@@ -1262,8 +1333,8 @@
 %    For that reason such code is not using the hook management, but
 %    instead private kernel commands directly before or after a public
 %    hook with the following naming
-%    convention: \cs{@kernel@before@\meta{hookname}} or
-%    \cs{@kernel@after@\meta{hookname}}. For example, in
+%    convention: \cs{@kernel@before@\meta{hook}} or
+%    \cs{@kernel@after@\meta{hook}}. For example, in
 %    \cs{enddocument} you find
 %\begin{verbatim}
 %   \UseHook{enddocument}%
@@ -1412,7 +1483,7 @@
 %
 %    The hooks are only executed if \cs{begin}\Arg{env} and
 %    \cs{end}\Arg{env} is used. If the environment code is executed
-%    via low-level calls to \cs{\meta{env}} and \cs{end\meta{env}}
+%    via low-level calls to \cs[no-index]{\meta{env}} and \cs[no-index]{end\meta{env}}
 %    (e.g., to avoid the environment grouping) they are not
 %    available. If you want them available in code using this method,
 %    you would need to add them yourself, i.e., write something like
@@ -1455,6 +1526,38 @@
 % \end{function}
 %
 %
+% \subsubsection{Generic hooks for commands}
+%
+%    Similar to environments there are now (at least in theory) two
+%    generic hooks available for any \LaTeX{} command. These are
+%    \begin{description}
+%    \item[\hook{cmd/\meta{name}/before}]
+%
+%       This hook is executed at the very start of the command
+%       execution.
+%
+%    \item[\hook{cmd/\meta{name}/after}]
+%       This hook is executed at the very end of the command body.  It is
+%       implemented as a reversed hook.
+%    \end{description}
+%    In practice there are restrictions and especially the
+%    \hook{after} hook works only with a subset of commands. Details
+%    about these restrictions are documented in
+%    \texttt{ltcmdhooks-doc.pdf} or with code in
+%    \texttt{ltcmdhooks-code.pdf}.
+%
+%
+%
+%
+% \subsubsection{Generic hooks provided by file loading operations}
+%
+%    There are several hooks added to \LaTeX{}'s process of loading
+%    file via its high-level interfaces such as \cs{input},
+%    \cs{include}, \cs{usepackage}, \cs{RequirePackage}, etc. These
+%    are documented in \texttt{ltfilehook-doc.pdf} or with code in
+%    \texttt{ltfilehook-code.pdf}.
+%
+%
 %
 % \subsubsection{Hooks provided by \cs{begin}\texttt{\{document\}}}
 % \label{sec:begindocument-hooks}
@@ -1554,7 +1657,9 @@
 %      generates material for further pages. It is the right place to
 %      do some final housekeeping and possibly write out some
 %      information to the \texttt{.aux} file (which is still open at
-%      this point to receive data). It is also the correct place to
+%      this point to receive data, but since there will be no more pages you
+%      need to write to it using \cs{immediate}\cs{write}). It is also the
+%      correct place to
 %      set up any testing code to be run when the \texttt{.aux} file
 %      is re-read in the next step.
 %
@@ -1621,7 +1726,7 @@
 %
 %
 %
-% \subsubsection{Hooks provided \cs{shipout} operations}
+% \subsubsection{Hooks provided by \cs{shipout} operations}
 % \label{sec:shipout}
 %
 %    There are several hooks and mechanisms added to \LaTeX{}'s
@@ -1630,14 +1735,6 @@
 %    \texttt{ltshipout-code.pdf}.
 %
 %
-% \subsubsection{Hooks provided by file loading operations}
-%
-%    There are several hooks added to \LaTeX{}'s
-%    process of loading file via its high-level interfaces such as
-%    \cs{input}, \cs{include}, \cs{usepackage}, etc. These are documented in
-%    \texttt{ltfilehook-doc.pdf} or with code in
-%    \texttt{ltfilehook-code.pdf}.
-%
 %
 % \subsubsection{Hooks provided in NFSS commands}
 %
@@ -1706,27 +1803,19 @@
 % \section{The Implementation}
 %
 %
-% \subsection{Loading further extensions}
-%
 %    \begin{macrocode}
 %<@@=hook>
 %    \end{macrocode}
 %
-%
-%    At the moment the whole module rolls back in one go, but if we
-%    make any modifications in later releases this will then need
-%    splitting.
+% \changes{v1.0i}{2021/03/18}
+%         {Use \cs{NewModuleRelease}.}
 %    \begin{macrocode}
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2020/10/01}%
-%<latexrelease>                 {\NewHook}{The hook management}%
-%    \end{macrocode}
-%    
-%    \begin{macrocode}
 \ExplSyntaxOn
+%<latexrelease>\NewModuleRelease{2020/10/01}{lthooks}
+%<latexrelease>                 {The~hook~management~system}
 %    \end{macrocode}
 %
-%
 %  \subsection{Debugging}
 %
 %  \begin{macro}{\g_@@_debug_bool}
@@ -1856,8 +1945,9 @@
 %    \end{macrocode}
 % \end{macro}
 %
-% \begin{macro}{\tl_gremove_once:Nx,\tl_show:x,\tl_log:x}
-%   Some variants of \pkg{expl3} functions. \fmi{should be moved to expl3}
+% \begin{macro}[int]{\tl_gremove_once:Nx,\tl_show:x,\tl_log:x}
+%   Some variants of \pkg{expl3} functions.
+%   \fmiinline{should probably be moved to expl3}
 %    \begin{macrocode}
 \cs_generate_variant:Nn \tl_gremove_once:Nn { Nx }
 \cs_generate_variant:Nn \tl_show:n { x }
@@ -1949,25 +2039,30 @@
 % \end{macro}
 %
 %
+%
 % \subsection{Providing new hooks}
 %
-% \begin{macro}{\g_@@_..._code_prop,\@@~...,\@@_next~...}
+% \subsubsection{The data structures of a hook}
 %
-%    Hooks have a \meta{name} and for each hook we have to provide a number of
-%    data structures. These are
+% \DescribeMacro{\g_@@_\meta{hook}_code_prop}
+% \DescribeMacro{\@@\textvisiblespace\meta{hook}}
+% \DescribeMacro{\@@_next\textvisiblespace\meta{hook}}
+%    Hooks have a name (called \meta{hook} in the description below)
+%    and for each hook we have to
+%    provide a number of data structures. These are
 %    \begin{description}
-%    \item[\cs{g_@@_\meta{name}_code_prop}] A property list holding the code
+%    \item[\cs{g_@@_\meta{hook}_code_prop}] A property list holding the code
 %    for the hook in separate chunks. The keys are by default the
 %    package names that add code to the hook, but it is possible
 %    for packages to define other keys. 
 %
-%    \item[{\cs[no-index]{g_@@_\meta{name}_rule_\meta{label1}\string|\meta{label2}_tl}}]
+%    \item[{\cs[no-index]{g_@@_\meta{hook}_rule_\meta{label1}\string|\meta{label2}_tl}}]
 %    A token list holding the relation between \meta{label1} and
-%    \meta{label2} in the \meta{name}.  The \meta{labels} are lexically
+%    \meta{label2} in the \meta{hook}.  The \meta{labels} are lexically
 %    (reverse) sorted to ensure that two labels always point to the same
-%    token list.  For global rules, the \meta{name} is |??|.
+%    token list.  For global rules, the \meta{hook} name is |??|.
 %
-%    \item[\cs{@@~\meta{name}}] The code that is actually executed
+%    \item[\cs{@@\textvisiblespace\meta{hook}}] The code that is actually executed
 %    when the hook is called in the document is stored in this token
 %    list. It is constructed from the code chunks applying the
 %    information.
@@ -1976,54 +2071,194 @@
 %    and to make it simpler to normalize hook names in
 %    \cs{@@_make_name:n}.
 %
-%    \item[\cs{g_@@_\meta{name}_reversed_tl}] Some hooks are
+%    \item[\cs{g_@@_\meta{hook}_reversed_tl}] Some hooks are
 %    \enquote{reversed}.  This token list stores a |-| for such hook
 %    so that it can be identified.  The |-| character is used because
 %    $\meta{reversed}1$ is $+1$ for normal hooks and $-1$ for reversed
 %    ones.
+
+%    \item[{\cs[no-index]{g_@@_\meta{hook}_declared_tl}}] This token
+%    list serves as marker for the hook being officially declared. Its
+%    existence is tested to raise an error in case another declaration
+%    is attempted.
 %
-%    \item[\cs{@@_toplevel~\meta{name}}] This token list stores the code
+%    \item[\cs{@@_toplevel\textvisiblespace\meta{hook}}] This token list stores the code
 %    inserted in the hook from the user's document, in the |top-level|
 %    label.  This label is special, and doesn't participate in sorting.
 %    Instead, all code is appended to it and executed after (or before,
 %    if the hook is reversed) the normal
 %    hook code, but before the |next| code chunk.
 %
-%    \item[\cs{@@_next~\meta{name}}] Finally there is extra code
-%    (normally empty) that is used on the next invocation of the hook
-%    (and then deleted). This can be used to define some special
-%    behavior for a single occasion from within the document.  This token
-%    list follows the same naming scheme than the main \cs{@@~\meta{name}}
-%    token list.  It is called \cs{@@_next~\meta{name}} rather than
-%    \cs{@@~next_\meta{name}} because otherwise a hook whose name is
-%    |next_|\meta{name} would clash with the next code-token list of the
-%    hook called \meta{name}.
+%    \item[\cs{@@_next\textvisiblespace\meta{hook}}] Finally there is
+%    extra code (normally empty) that is used on the next invocation
+%    of the hook (and then deleted). This can be used to define some
+%    special behavior for a single occasion from within the document.
+%    This token list follows the same naming scheme than the main
+%    \cs{@@\textvisiblespace\meta{hook}} token list.  It is called
+%    \cs{@@_next\textvisiblespace\meta{hook}} rather than
+%    \cs[no-index]{@@\textvisiblespace next_\meta{hook}} because
+%    otherwise a hook whose name is |next_|\meta{hook} would clash
+%    with the next code-token list of the hook called \meta{hook}.
 %
 %    \end{description}
-%  \end{macro}
 %
 %
+% \subsubsection{On the existence of hooks}
+% \label{sec:existence}
+%
+%    A hook may be in different states of existence. Here we give an
+%    overview of internal commands to set up hooks and explain how the
+%    different states are distinguished. The actual implementation
+%    then follows in the next sections.
+%
+%    One problem we have to solve is, that we need to be able to add
+%    code to hooks (e.g., with \cs{AddToHook}) even if that code has
+%    not been declared yet. For example, one package needs to write
+%    into a hook of another package, but that package ay not get
+%    loaded or only loaded later. Another problem most hooks require
+%    declaration but this is not the case for the generic hooks.
+%
+%    We therefore distinguish the following states for a hook and they
+%    are managed with four different tests: structure existence
+%    (\cs{@@_if_structure_exist:nTF}), creation
+%    (\cs{@@_if_usable:nTF}), declaration (\cs{@@_if_declared:nTF})
+%    and disabled or not (\cs{@@_if_disabled:nTF})
+%    \begin{description}
+%    \setlist[itemize]{leftmargin=5cm,format=\cs}
+%    \item[not existing]
+%
+%       Nothing is known about the hook so far. This state can be
+%       detected with \cs{@@_if_structure_exist:nTF}
+%       (which uses the  false branch).
+%
+%       In this state the hook can be declared, disabled, rules can be
+%       defined or code could be added to it, but it is not possible
+%       to use the hook (with \cs{UseHook}).
+
+%    \item[basic data structure set up]
+%
+%       A hook is this state when its basic data structure has been
+%       set up (using \cs{@@_init_structure:n}). The data structure setup happens
+%       automatically when commands such as \cs{AddToHook}  are used
+%       and the hook is at that point in state \enquote{not existing}.
+%
+%       In this state the four tests give the following results:
+%     \begin{itemize}
+%       \item [@@_if_structure_exist:nTF]      returns |true|.
+%       \item [@@_if_usable:nTF]   returns |false|.
+%       \item [@@_if_declared:nTF]  returns |false|.
+%       \item [@@_if_disabled:nTF]  returns |false|.
+%     \end{itemize}
+%
+%       The allowed acctions are the same as in the \enquote{not
+%       existing} state.
+%
+%    \item[declared]
+%
+%       A hook is in this state it is not disabled and was explicity declared (e.g.,
+%       with \cs{NewHook}). In this case the four tests give the
+%       following results:
+%     \begin{itemize}
+%       \item [@@_if_structure_exist:nTF]      returns |true|.
+%       \item [@@_if_usable:nTF]   returns |true|.
+%       \item [@@_if_declared:nTF]  returns |true|.
+%       \item [@@_if_disabled:nTF]  returns |false|.
+%     \end{itemize}
+%
+%    \item[usable]
+%
+%       A hook is in this state if it is not disabled, was not
+%       explicitly declared but nevertheless is allowed to be used
+%       (with \cs{UseHook} or \cs{hook_use:n}). This state is only
+%       possible for generic hooks as they do not need to be
+%       declared. Therefore such hooks move directly from state
+%       \enquote{not existing} to \enquote{usable} the moment a
+%       declaration such as \cs{AddToHook} wants to add to the hook
+%       data structure.  In this state the tests give the following
+%       results:
+%     \begin{itemize}
+%       \item [@@_if_structure_exist:nTF]      returns |true|.
+%       \item [@@_if_usable:nTF]   returns |true|.
+%       \item [@@_if_declared:nTF]  returns |false|.
+%       \item [@@_if_disabled:nTF]  returns |false|.
+%     \end{itemize}
+%
+%
+%    \item[disabled]
+%
+%       A hook in any state is moved to this state when
+%       \cs{DisableHook} is used. This changes the tests to give the
+%       following results:
+%     \begin{itemize}
+%       \item [@@_if_structure_exist:nTF]      \emph{unchanged}.
+%       \item [@@_if_usable:nTF]   returns |false|.
+%       \item [@@_if_declared:nTF]  returns |true|.
+%       \item [@@_if_disabled:nTF]  returns |true|.
+%     \end{itemize}
+%       The  structure test is unchanged (if the hook was unknown before it is
+%       false, otherwise true). The usable test returns false so that
+%       any \cs{UseHook} will bypass the hook from now on. The
+%       declared test returns true so that any further \cs{NewHook}
+%       generates an error and the disabled test returns true so that
+%       \cs{AddToHook} can return an error.
+% \fmiinline{maybe it should do this only after begin document?}
+%
+%    \end{description}
+%
+%
+%
+%
+% \subsubsection{Setting hooks up}
 %
 %
-%  \begin{macro}{\hook_new:n}
-%    The \cs{hook_new:n} declaration declare a new hook and expects
+%  \begin{macro}{\hook_new:n,\@@_new:n}
+%    The \cs{hook_new:n} declaration declares a new hook and expects
 %    the hook \meta{name} as its argument, e.g.,
 %    \hook{begindocument}.
 %    \begin{macrocode}
 \cs_new_protected:Npn \hook_new:n #1
   { \@@_normalize_hook_args:Nn \@@_new:n {#1} }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 \cs_new_protected:Npn \@@_new:n #1
   {
 %    \end{macrocode}
-%    We check for one of the internal data structures and if it
-%    already exists we complain.
+%   We check if the hook was already \emph{explicitly} declared with
+%   \cs{hook_new:n}, and if it already exists we complain, otherwise set
+%   the \enquote{created} flag for the hook so that it errors next time
+%   \cs{hook_new:n} is used.
+%    \begin{macrocode}
+    \@@_if_declared:nTF {#1}
+      { \__kernel_msg_error:nnn { hooks } { exists } {#1} }
+      {
+        \tl_new:c { g_@@_#1_declared_tl }
+        \@@_make_usable:n {#1}
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+%
+%  
+%  
+%  \begin{macro}{\@@_make_usable:n}
+%
+%    This initializes all hook data structures for the hook but if
+%    used on its own doesn't mark the hook as declared (as
+%    \cs{hook_new:n} does, so a later \cs{hook_new:n} on that hook will
+%    not result in an error.  This command is internally used by
+%    \cs{hook_gput_code:n} when adding code to a generic hook.
 %    \begin{macrocode}
-    \hook_if_exist:nTF {#1}
-      { \msg_error:nnn { hooks } { exists } {#1} }
+\cs_new_protected:Npn \@@_make_usable:n #1
+  {
 %    \end{macrocode}
-%    Otherwise we add the hook name to the list of all hooks and
-%    allocate the necessary data structures for the new hook.
+%   Now we check if the hook's data structure can be safely created
+%   without \pkg{expl3} raising errors, then
+%   we add the hook name to the list of all hooks and
+%   allocate the necessary data structures for the new hook,
+%   otherwise just do nothing.
 %    \begin{macrocode}
+    \tl_if_exist:cF { @@~#1 }
       {
         \seq_gput_right:Nn \g_@@_all_seq {#1}
 %    \end{macrocode}
@@ -2034,12 +2269,12 @@
 %    \end{macrocode}
 %    Now ensure that the base data structure for the hook exists:
 %    \begin{macrocode}
-        \@@_declare:n {#1}
+        \@@_init_structure:n {#1}
 %    \end{macrocode}
 %    The \cs{g_@@_\meta{hook}_labels_clist} holds the sorted list of
 %    labels (once it got sorted). This is used only for debugging.
 %    \begin{macrocode}
-        \clist_new:c {g_@@_#1_labels_clist}
+        \clist_new:c { g_@@_#1_labels_clist }
 %    \end{macrocode}
 %    Some hooks should reverse the default order of code chunks. To
 %    signal this we have a token list which is empty for normal hooks
@@ -2061,23 +2296,30 @@
 %
 %    \begin{macrocode}
         \@@_include_legacy_code_chunk:n {#1}
-     }
+      }
   }
 %    \end{macrocode}
 %  \end{macro}
 %
 %
 %
-% \begin{macro}{\@@_declare:n}
-%   This function declares the basic data structures for a hook without
-%   actually declaring the hook itself.  This is needed to allow adding
-%   to undeclared hooks.  Here it is unnecessary to check whether all
-%   variables exist, since all three are declared at the same time
-%   (either all of them exist, or none).
+% \begin{macro}{\@@_init_structure:n}
+%    This function declares the basic data structures for a hook
+%    without explicit declaring the hook itself.  This is needed to
+%    allow adding to undeclared hooks.  Here it is unnecessary to
+%    check whether all variables exist, since all three are declared
+%    at the same time (either all of them exist, or none).
+%
+%    It creates the hook code pool
+%    (\cs[no-index]{g_@@_\meta{hook}_code_prop}) and the |top-level|
+%    and |next| token lists.  A hook is initialized with
+%    \cs{@@_init_structure:n} the first time anything is added to it.
+%    Inizializing a hook just with \cs{@@_init_structure:n} will not
+%    make it usable with \cs{hook_use:n}.
 %    \begin{macrocode}
-\cs_new_protected:Npn \@@_declare:n #1
+\cs_new_protected:Npn \@@_init_structure:n #1
   {
-    \@@_if_exist:nF {#1}
+    \@@_if_structure_exist:nF {#1}
       {
         \prop_new:c { g_@@_#1_code_prop }
         \tl_new:c { @@_toplevel~#1 }
@@ -2109,6 +2351,9 @@
 %    \end{macrocode}
 %  \end{macro}
 %
+%
+%
+%
 %  \begin{macro}{\hook_new_pair:nn}
 %    A shorthand for declaring a normal and a (matching) reversed hook in one go.
 %    \begin{macrocode}
@@ -2159,6 +2404,140 @@
 %
 %
 %
+% \subsubsection{Disabling and providing hooks}
+%
+% \begin{macro}{\hook_disable:n}
+% \begin{macro}{\@@_disable:n}
+% \begin{macro}[pTF]{\@@_if_disabled:n}
+%
+%    Disables a hook by creating its
+%    \cs[no-index]{g_@@_\meta{hook}_declared_tl} so that the hook
+%    errors when used with \cs{hook_new:n}, then it undefines
+%    \cs{@@\textvisiblespace\meta{hook}} so that it may not be executed.
+%
+%    This does not clear any code that may be already stored in the
+%    hook's structure, but doesn't allow adding more code.
+%    \cs{@@_if_disabled:nTF} uses that specific combination to check
+%    if the hook is disabled.
+%
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>         {\hook_disable:n}{Disable~hooks}
+%    \end{macrocode}
+%    
+%    \begin{macrocode}
+\cs_new_protected:Npn \hook_disable:n #1
+  { \@@_normalize_hook_args:Nn \@@_disable:n {#1} }
+\cs_new_protected:Npn \@@_disable:n #1
+  {
+    \tl_gclear_new:c { g_@@_#1_declared_tl }
+    \cs_undefine:c { @@~#1 }
+  }
+\prg_new_conditional:Npnn \@@_if_disabled:n #1 { p, T, F, TF }
+  {
+    \bool_lazy_and:nnTF
+        { \tl_if_exist_p:c { g_@@_#1_declared_tl } }
+        { ! \tl_if_exist_p:c { @@~#1 } }
+      { \prg_return_true: }
+      { \prg_return_false: }
+  }
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2020/10/01}
+%<latexrelease>                 {\hook_disable:n}{Disable~hooks}
+%<latexrelease>
+%<latexrelease>\cs_new_protected:Npn \hook_disable:n #1 {}
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\hook_provide:n}
+% \begin{macro}{\hook_provide_reversed:n}
+% \begin{macro}{\@@_provide:n}
+%    The \cs{hook_provide:n} declaration declares a new hook if it
+%    wasn't declared already, in which case it only checks that the
+%    already existing hook is not a reversed hook.
+%    The \cs{hook_provide_reversed:n} does the same for reversed hooks.
+%    \hook{begindocument}.
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>         {\hook_provide:n}{Providing~hooks}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\cs_new_protected:Npn \hook_provide:n #1
+  { \@@_normalize_hook_args:Nn \@@_provide:nn {#1} {   } }
+\cs_new_protected:Npn \hook_provide_reversed:n #1
+  { \@@_normalize_hook_args:Nn \@@_provide:nn {#1} { - } }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_provide:nn #1 #2
+  {
+%    \end{macrocode}
+%    If the hook to be provided was disabled we warn (for now --- this
+%    may change).
+%    \begin{macrocode}
+    \@@_if_disabled:nTF {#1}
+      { \__kernel_msg_warning:nnn { hooks } { provide-disabled } {#1} }
+%    \end{macrocode}
+%    Otherwise we check if it was already declared.
+%    \begin{macrocode}
+      {
+        \@@_if_declared:nTF {#1}
+          {
+%    \end{macrocode}
+%    Issue an error if we try to provide a a hook that is reversed and
+%    the already existing one is not (or vice versa).
+%    \begin{macrocode}
+            \str_if_eq:eeF { \tl_use:c { g_@@_#1_reversed_tl } } {#2}
+              { \__kernel_msg_error:nnn { hooks } { provide-error } {#1} }
+          }
+%    \end{macrocode}
+%    If it wasn't declared, we declared as a normal or reversed hook
+%    as appropriate.
+%    \begin{macrocode}
+          {
+            \tl_new:c { g_@@_#1_declared_tl }
+            \@@_make_usable:n {#1}
+            \tl_gset:cn { g_@@_#1_reversed_tl } {#2}
+          }
+      }
+  }
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+% \begin{macro}{\hook_provide_pair:nn}
+%    A shorthand for providing a normal and a (matching) reversed hook in one go.
+%    \begin{macrocode}
+\cs_new_protected:Npn \hook_provide_pair:nn #1#2
+  { \hook_provide:n {#1} \hook_provide_reversed:n {#2} }
+%    \end{macrocode}
+% \end{macro}
+%
+%    \begin{macrocode}
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2020/10/01}
+%<latexrelease>                 {\hook_provide:n}{Providing~hooks}
+%<latexrelease>
+%<latexrelease>\cs_new_protected:Npn \hook_provide_reversed:n #1 {}
+%<latexrelease>\cs_new_protected:Npn \hook_provide:n #1 {}
+%<latexrelease>\cs_new_protected:Npn \hook_provide_pair:nn #1#2 {}
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%
+%
 % \subsection{Parsing a label}
 %
 % \begin{macro}[EXP]{\@@_parse_label_default:n}
@@ -2193,7 +2572,7 @@
   {
     \tl_if_empty:nTF {#1}
       {
-        \msg_expandable_error:nn { hooks } { empty-label }
+        \__kernel_msg_expandable_error:nn { hooks } { empty-label }
         \@@_currname_or_default:
       }
       {
@@ -2230,7 +2609,7 @@
       {
         \tl_if_empty:NTF \@currname
           {
-            \msg_expandable_error:nnn { hooks } { should-not-happen }
+            \__kernel_msg_expandable_error:nnn { hooks } { should-not-happen }
               { Empty~default~label. }
             \@@_make_name:n { label-missing }
           }
@@ -2247,10 +2626,10 @@
 %   then uses \cs{cs_to_str:N} to get the string representation of that,
 %   without the escape character.  \cs{cs:w}-based expansion is used
 %   instead of |e|-based because Unicode characters don't behave well
-%   inside \cs{expanded}.  The macro adds the \cs{@@~} prefix to the
+%   inside \cs{expanded}.  The macro adds the \cs[no-index]{@@\textvisiblespace} prefix to the
 %   hook name to reuse the hook's code token list to build the csname
 %   and avoid leaving \enquote{public} control sequences defined
-%   (as~\cs{relax}) in TeX's memory.
+%   (as~\cs[no-index]{relax}) in TeX's memory.
 %    \begin{macrocode}
 \cs_new:Npn \@@_make_name:n #1
   {
@@ -2310,6 +2689,9 @@
 % \end{macro}
 %
 %
+%
+% \subsection{Adding or removing hook code}
+%
 % \begin{macro}{\hook_gput_code:nnn}
 % \begin{macro}{\@@_gput_code:nnn,\@@_gput_code:nxv,\@@_hook_gput_code_do:nnn}
 %
@@ -2319,6 +2701,9 @@
 %    \begin{macrocode}
 \cs_new_protected:Npn \hook_gput_code:nnn #1 #2
   { \@@_normalize_hook_args:Nnn \@@_gput_code:nnn {#1} {#2} }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 \cs_new_protected:Npn \@@_gput_code:nnn #1 #2 #3
   {
 %    \end{macrocode}
@@ -2342,7 +2727,7 @@
 %    If no removal is queued, we are free to add.  Start by checking if
 %    the hook exists.
 %    \begin{macrocode}
-            \hook_if_exist:nTF {#1}
+            \@@_if_usable:nTF {#1}
 %    \end{macrocode}
 %    If so we simply add (or append) the new code to the property list
 %    holding different chunks for the hook. At \verb=\begin{document}=
@@ -2363,10 +2748,17 @@
 %    declare it as a generic hook, if its name matches one of the valid
 %    patterns.
 %    \begin{macrocode}
-              { \@@_try_declaring_generic_hook:nnn {#1} {#2} {#3} }
+              {
+                \@@_if_disabled:nTF {#1}
+                  { \__kernel_msg_error:nnn { hooks } { hook-disabled } {#1} }
+                  { \@@_try_declaring_generic_hook:nnn {#1} {#2} {#3} }
+              }
           }
       }
   }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 \cs_generate_variant:Nn \@@_gput_code:nnn { nxv }
 %    \end{macrocode}
 %
@@ -2378,7 +2770,7 @@
 %    However, first some debugging info if debugging is enabled:
 %    \begin{macrocode}
     \@@_debug:n{\iow_term:x{****~ Add~ to~
-                      \hook_if_exist:nF {#1} { undeclared~ }
+                      \@@_if_usable:nF {#1} { undeclared~ }
                       hook~ #1~ (#2)
                       \on@line\space <-~ \tl_to_str:n{#3}} }
 %    \end{macrocode}
@@ -2386,9 +2778,9 @@
 %    If there's code already there, then append \verb=#3= to that,
 %    otherwise just put \verb=#3=.  If the current label is |top-level|,
 %    the code is added to a dedicated token list
-%    \cs[no-index]{@@_toplevel~\meta{hook}} that goes at the end of the
+%    \cs{@@_toplevel\textvisiblespace\meta{hook}} that goes at the end of the
 %    hook (or at the beginning, for a reversed hook), just before
-%   \cs[no-index]{@@_next~\meta{hook}}.
+%   \cs[no-index]{@@_next\textvisiblespace\meta{hook}}.
 %    \begin{macrocode}
     \str_if_eq:nnTF {#2} { top-level }
       {
@@ -2396,12 +2788,12 @@
           {
 %    \end{macrocode}
 %    If the hook's basic structure does not exist, we need to declare it
-%    with \cs{@@_declare:n}.
+%    with \cs{@@_init_structure:n}.
 %    \begin{macrocode}
-            \@@_declare:n {#1}
+            \@@_init_structure:n {#1}
             \@@_tl_gput_right:cn { @@_toplevel~#1 } {#3}
           }
-          { \msg_error:nnn { hooks } { misused-top-level } {#1} }
+          { \__kernel_msg_error:nnn { hooks } { misused-top-level } {#1} }
       }
       {
         \prop_get:cnNTF { g_@@_#1_code_prop } {#2} \l_@@_return_tl
@@ -2423,14 +2815,15 @@
 %    \begin{macrocode}
 \cs_new_protected:Npn \@@_gput_undeclared_hook:nnn #1 #2 #3
   {
-    \@@_declare:n {#1}
+    \@@_init_structure:n {#1}
     \@@_hook_gput_code_do:nnn {#1} {#2} {#3}
   }
 %    \end{macrocode}
 % \end{macro}
 %
-% \begin{macro}{\@@_try_declaring_generic_hook:nnn}
-% \begin{macro}{\@@_try_declaring_generic_next_hook:nn}
+% \begin{macro}{\@@_try_declaring_generic_hook:nnn,
+%               \@@_try_declaring_generic_next_hook:nn}
+%
 %   These entry-level macros just pass the arguments along to the
 %   common \cs{@@_try_declaring_generic_hook:nNNnn} with the right
 %   functions to execute when some action is to be taken.
@@ -2457,13 +2850,14 @@
       \hook_gput_next_code:nn \@@_gput_next_do:nn
   }
 %    \end{macrocode}
+% \end{macro}
 %
-% \begin{macro}{
-%     \@@_try_declaring_generic_hook:nNNnn,
-%     \@@_try_declaring_generic_hook_split:nNNnn
-%   }
-% \begin{macro}[TF]{\@@_try_declaring_generic_hook:wn}
-%   \cs{@@_try_declaring_generic_hook:nNNnn} now splits the hook name
+%
+% \begin{macro}{\@@_try_declaring_generic_hook:nNNnn,
+%               \@@_try_declaring_generic_hook_split:nNNnn}
+%
+%   \cs{@@_try_declaring_generic_hook:nNNnn}
+%   now splits the hook name
 %   at the first \texttt{/} (if any) and first checks if it is a
 %   file-specific hook (they require some normalization) using
 %   \cs{@@_if_file_hook:wTF}. If not then check it is one of a
@@ -2481,12 +2875,24 @@
       }
       { \@@_try_declaring_generic_hook_split:nNNnn {#1} }
   }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 \cs_new_protected:Npn \@@_try_declaring_generic_hook_split:nNNnn #1 #2 #3
   {
     \@@_try_declaring_generic_hook:wnTF #1 / / / \scan_stop: {#1}
       { #2 }
       { #3 } {#1}
   }
+%    \end{macrocode}
+% \end{macro}
+%
+%
+% \begin{macro}[TF]{\@@_try_declaring_generic_hook:wn}
+%
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>         {\@@_try_declaring_generic_hook:wn}{Support~cmd~hooks}
 \prg_new_protected_conditional:Npnn \@@_try_declaring_generic_hook:wn
     #1 / #2 / #3 / #4 \scan_stop: #5 { TF }
   {
@@ -2495,31 +2901,70 @@
       {
         \prop_if_in:NnTF \c_@@_generics_prop {#1}
           {
-            \hook_if_exist:nF {#5} { \hook_new:n {#5} }
+            \@@_if_usable:nF {#5}
+              {
+%    \end{macrocode}
+%    If the hook doesn't exist yet we check if it is a \texttt{cmd}
+%    hook and if so we attempt patching the command in addition to
+%    declaring the hook.
+%
+%    For some commands this will not be possible, in which case
+%    \cs{@@_patch_cmd_or_delay:Nnn} (defined in \texttt{ltcmdhooks})
+%    will generate an appropriate error message.
+%    \begin{macrocode}
+                \str_if_eq:nnT {#1} { cmd }
+                  { \@@_try_put_cmd_hook:n {#5} }
 %    \end{macrocode}
-%    After having declared the hook we check the second component (for
-%    file hooks) or the third component for environment hooks) and
-%    if it is on the list of components for which we should have declared
-%    a reversed hook we alter the hook data structure accordingly.
+%
+%    Declare the hook always even if it can't really be used (error
+%    message generated elsewhere).
+%
+%    Here we use \cs{@@_make_usable:n}, so that a \cs{hook_new:n} is still
+%    possible later.
 %    \begin{macrocode}
+                \@@_make_usable:n {#5}
+              }
             \prop_if_in:NnTF \c_@@_generics_reversed_ii_prop {#2}
               { \tl_gset:cn { g_@@_#5_reversed_tl } { - } }
               {
                 \prop_if_in:NnT \c_@@_generics_reversed_iii_prop {#3}
                   { \tl_gset:cn { g_@@_#5_reversed_tl } { - } }
               }
-%    \end{macrocode}
-%    Now that we know that the hook is declared we can add the code to it.
-%    \begin{macrocode}
             \prg_return_true:
           }
           { \prg_return_false: }
       }
   }
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2020/10/01}%
+%<latexrelease>         {\@@_try_declaring_generic_hook:wn}{Support~cmd~hooks}
+%<latexrelease>
+%<latexrelease>\prg_new_protected_conditional:Npnn \@@_try_declaring_generic_hook:wn
+%<latexrelease>    #1 / #2 / #3 / #4 \scan_stop: #5 { TF }
+%<latexrelease>  {
+%<latexrelease>    \tl_if_empty:nTF {#2}
+%<latexrelease>      { \prg_return_false: }
+%<latexrelease>      {
+%<latexrelease>        \prop_if_in:NnTF \c_@@_generics_prop {#1}
+%<latexrelease>          {
+%<latexrelease>            \@@_if_declared:nF {#5} { \hook_new:n {#5} }
+%<latexrelease>            \prop_if_in:NnTF \c_@@_generics_reversed_ii_prop {#2}
+%<latexrelease>              { \tl_gset:cn { g_@@_#5_reversed_tl } { - } }
+%<latexrelease>              {
+%<latexrelease>                \prop_if_in:NnT \c_@@_generics_reversed_iii_prop {#3}
+%<latexrelease>                  { \tl_gset:cn { g_@@_#5_reversed_tl } { - } }
+%<latexrelease>              }
+%<latexrelease>            \prg_return_true:
+%<latexrelease>          }
+%<latexrelease>          { \prg_return_false: }
+%<latexrelease>      }
+%<latexrelease>  }
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
 %    \end{macrocode}
-% \end{macro}
-% \end{macro}
-% \end{macro}
 % \end{macro}
 %
 % \begin{macro}[pTF]{\@@_if_file_hook:w}
@@ -2528,7 +2973,7 @@
 %   |file/before/foo.tex|).  If it is a file-specific hook, then it
 %   executes the \meta{true} branch, otherwise \meta{false}.
 %
-%   A file-specific hook is \texttt{file/\meta{position}/\meta{name}}.
+%   A file-specific hook is \hook{file/\meta{position}/\meta{name}}.
 %   If any of these parts don't exist, it is a general file hook or not
 %   a file hook at all, so the conditional evaluates to \meta{false}.
 %   Otherwise, it checks that the first part is |file| and that the
@@ -2594,14 +3039,16 @@
 %    Property list holding the generic names. We don't provide any user
 %    interface to this as this is meant to be static.
 %    \begin{description}
+%    \item[\texttt{cmd}]
+%      The generic hooks used for commands.
 %    \item[\texttt{env}]
 %      The generic hooks used in \cs{begin} and \cs{end}.
-%    \item[\texttt{file}]
+%    \item[\texttt{file}, \texttt{package}, \texttt{class}, \texttt{include}]
 %      The generic hooks used when loading a file
 %    \end{description}
 %    \begin{macrocode}
 \prop_const_from_keyval:Nn \c_@@_generics_prop
-  {env=,file=,package=,class=,include=}
+     {cmd=,env=,file=,package=,class=,include=}
 %    \end{macrocode}
 %  \end{macro}
 %
@@ -2628,11 +3075,11 @@
 \cs_new_protected:Npn \@@_gremove_code:nn #1 #2
   {
 %    \end{macrocode}
-%    First check that the hook code pool exists.  \cs{hook_if_exist:nTF}
+%    First check that the hook code pool exists.  \cs{@@_if_usable:nTF}
 %    isn't used here because it should be possible to remove code from a
 %    hook before its defined (see section~\ref{sec:querying}).
 %    \begin{macrocode}
-    \@@_if_exist:nTF {#1}
+    \@@_if_structure_exist:nTF {#1}
       {
 %    \end{macrocode}
 %    Then remove the chunk and run \cs{@@_update_hook_code:n} so
@@ -2640,9 +3087,9 @@
 %    \verb=\begin{document}=.
 %
 %    If all code is to be removed, clear the code pool
-%    \cs[no-index]{g_@@_\meta{hook}_code_prop}, the top-level code
-%    \cs[no-index]{@@_toplevel~\meta{hook}}, and the next-execution code
-%    \cs[no-index]{@@_next~\meta{hook}}.
+%    \cs{g_@@_\meta{hook}_code_prop}, the top-level code
+%    \cs{@@_toplevel\textvisiblespace\meta{hook}}, and the next-execution code
+%    \cs{@@_next\textvisiblespace\meta{hook}}.
 %    \begin{macrocode}
         \str_if_eq:nnTF {#2} {*}
           {
@@ -2655,7 +3102,7 @@
 %    If the label is |top-level| then clear the token list, as all code
 %    there is under the same label.  Marked removal is not implemented
 %    for |top-level| because it is hard to reliably know that no code
-%    was added to \cs[no-index]{@@_toplevel~\meta{hook}} (granted that
+%    was added to \cs{@@_toplevel\textvisiblespace\meta{hook}} (granted that
 %    an empty code could be interpreted as that, but then it differs in
 %    behaviour from other labels, in which an empty chunk is still valid
 %    for removal).  Besides, it doesn't make much (if any) sense for
@@ -2679,7 +3126,7 @@
 %    \end{macrocode}
 %    Finally update the code, if the hook exists.
 %    \begin{macrocode}
-        \hook_if_exist:nT {#1}
+        \@@_if_usable:nT {#1}
           { \@@_update_hook_code:n {#1} }
       }
 %    \end{macrocode}
@@ -2774,10 +3221,10 @@
 %    disadvantage of that being not really distinguishable from a real
 %    hook name. I now have settled for \texttt{??} which needs some
 %    gymnastics to get it into the csname, but since this is used a
-%    lot things should be fast, so this is not done with \texttt{c}
+%    lot, the code should be fast, so this is not done with \texttt{c}
 %    expansion in the code later on.
 %
-%    \cs{@@~??} isn't used, but it has to be defined to trick
+%    \cs{@@\textvisiblespace??} isn't used, but it has to be defined to trick
 %    the code into thinking that \verb=??= is actually a hook.
 %    \begin{macrocode}
 \prop_new:c {g_@@_??_code_prop}
@@ -2798,14 +3245,12 @@
 %
 %  \begin{macro}{\hook_gset_rule:nnnn}
 %  \begin{macro}{\@@_gset_rule:nnnn}
-%
-%    \fmi{needs docu correction given new implementation}
-%
 %    With
 %    \cs{hook_gset_rule:nnnn}\Arg{hook}\Arg{label1}\Arg{relation}\Arg{label2}
 %    a relation is defined between the two code labels for the given
 %    \meta{hook}.  The special hook \texttt{??} stands for \emph{any}
-%    hook describing a default rule.
+%    hook, which sets a default rule (to be used if no other relation
+%    between the two hooks exist).
 %    \begin{macrocode}
 \cs_new_protected:Npn \hook_gset_rule:nnnn #1#2#3#4
   {
@@ -2813,14 +3258,14 @@
       {#1} {#2} {#3} {#4}
   }
 %    \end{macrocode}
-%    
+%
 %    \begin{macrocode}
 \cs_new_protected:Npn \@@_gset_rule:nnnn #1#2#3#4
   {
 %    \end{macrocode}
 %    First we ensure the basic data structure of the hook exists:
 %    \begin{macrocode}
-    \@@_declare:n {#1}
+    \@@_init_structure:n {#1}
 %    \end{macrocode}
 %    Then we clear any previous relationship between both labels.
 %    \begin{macrocode}
@@ -2834,7 +3279,7 @@
           {#1} {#2} {#4}
         \@@_update_hook_code:n {#1}
       }
-      { \msg_error:nnnnnn { hooks } { unknown-rule }
+      { \__kernel_msg_error:nnnnnn { hooks } { unknown-rule }
                           {#1} {#2} {#3} {#4}        }
   }
 %    \end{macrocode}
@@ -2938,7 +3383,7 @@
   {
     \if_int_compare:w \@@_str_compare:nn {#1} {#2} > 0 \exp_stop_f:
       \prg_return_true:
-    \else
+    \else:
       \prg_return_false:
     \fi:
   }
@@ -3038,13 +3483,13 @@
 %    If there aren't any code
 %    chunks for the current hook, there is no point in even starting
 %    the sorting routine so we make a quick test for that and in that
-%    case just update \cs{@@~\meta{hook}} to hold the |top-level| and
+%    case just update \cs{@@\textvisiblespace\meta{hook}} to hold the |top-level| and
 %    |next| code chunks. If there are code chunks we call
 %    \cs{@@_initialize_single:NNn} and pass to it ready made csnames
 %    as they are needed several times inside. This way we save a bit
 %    on processing time if we do that up front.
 %    \begin{macrocode}
-    \hook_if_exist:nT {#1}
+    \@@_if_usable:nT {#1}
       {
         \prop_if_empty:cTF {g_@@_#1_code_prop}
           {
@@ -3097,7 +3542,7 @@
 % \begin{macro}[EXP]{\@@_tl_csname:n,\@@_seq_csname:n}
 %   It is faster to pass a single token and expand it when necessary
 %   than to pass a bunch of character tokens around.
-%   \fmi{note to myself: verify}
+%   \fmiinline{note to myself: verify}
 %    \begin{macrocode}
 \cs_new:Npn \@@_tl_csname:n #1 { l_@@_label_#1_tl }
 \cs_new:Npn \@@_seq_csname:n #1 { l_@@_label_#1_seq }
@@ -3161,7 +3606,7 @@
 %    a way that one can omit a lot of tests and I have mimicked that as
 %    far as possible. The result is a restriction I do not test for at
 %    the moment: a label can't be equal to the number 0!  \fmi{Needs
-%    checking for, just in case}
+%    checking for, just in case ... maybe}
 %
 %    ^^A #1 <- \@@~#1
 %    ^^A #2 <- \g_@@_#1_labels_clist
@@ -3302,7 +3747,7 @@
 %    \end{macrocode}
 %
 %    This is not really the information one needs in the error case
-%    but will do for now \ldots \fmi{fix}
+%    but will do for now \ldots \fmi{improve output on a rainy day}
 %    \begin{macrocode}
         \@@_debug_label_data:N \l_@@_work_prop
         \iow_term:x{====================}
@@ -3442,7 +3887,7 @@
 \cs_new_protected:cpn { @@_apply_rule_xE:nnn } #1#2#3
   {
     \@@_debug:n { \@@_msg_pair_found:nnn {#1} {#2} {#3} }
-    \msg_error:nnnnnn { hooks } { labels-incompatible }
+    \__kernel_msg_error:nnnnnn { hooks } { labels-incompatible }
       {#1} {#2} {#3} { 1 }
     \use:c { @@_apply_rule_->:nnn } {#1} {#2} {#3}
     \use:c { @@_apply_rule_<-:nnn } {#1} {#2} {#3}
@@ -3450,7 +3895,7 @@
 \cs_new_protected:cpn { @@_apply_rule_xW:nnn } #1#2#3
   {
     \@@_debug:n { \@@_msg_pair_found:nnn {#1} {#2} {#3} }
-    \msg_warning:nnnnnn { hooks } { labels-incompatible }
+    \__kernel_msg_warning:nnnnnn { hooks } { labels-incompatible }
       {#1} {#2} {#3} { 0 }
   }
 %    \end{macrocode}
@@ -3573,15 +4018,20 @@
   { \@@_log_cmd:x { >~#1 } }
 \cs_new_protected:Npn \@@_log_line_indent:x #1
   { \@@_log_cmd:x { >~\@spaces #1 } }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 \cs_new_protected:Npn \@@_log:nN #1 #2
   {
     \@@_preamble_hook:n {#1}
     \@@_log_cmd:x { ^^J ->~The~hook~'#1': }
 %    \end{macrocode}
-%    
+%
 %    \begin{macrocode}
-    \hook_if_exist:nF {#1}
-      { \@@_log_line:x { is~not~declared! } }
+    \@@_if_usable:nF {#1}
+      { \@@_log_line:x { The~hook~is~not~declared. } }
+    \@@_if_disabled:nT {#1}
+      { \@@_log_line:x { The~hook~is~disabled. } }
     \hook_if_empty:nTF {#1}
       { #2 { The~hook~is~empty } }
       {
@@ -3599,7 +4049,7 @@
         \@@_log_line:x
           {
             Document-level~(top-level)~code
-            \hook_if_exist:nT {#1}
+            \@@_if_usable:nT {#1}
               { ~(executed~\@@_if_reversed:nTF {#1} {first} {last} ) } :
           }
         \@@_log_line_indent:x
@@ -3650,7 +4100,7 @@
 %   to that hook) and not empty
 %    \begin{macrocode}
         \bool_lazy_and:nnTF
-            { \hook_if_exist_p:n {#1} }
+            { \@@_if_usable_p:n {#1} }
             { ! \hook_if_empty_p:n {#1} }
           {
             \@@_log_line:x
@@ -3672,10 +4122,12 @@
               }
           }
           {
+            \@@_log_line:x { Execution~order: }
             #2
               {
-                Hook~ \hook_if_exist:nTF {#1}
-                  {code~pool~empty} {not~declared}
+                \@spaces Not~set~because~the~hook~ \@@_if_usable:nTF {#1}
+                  { code~pool~is~empty }
+                  { is~\@@_if_disabled:nTF {#1} {disabled} {undeclared} }
               }
           }
       }
@@ -3767,25 +4219,37 @@
 %    \end{macrocode}
 % \end{macro}
 %
+%
+%
+%
 %  \subsection{Specifying code for next invocation}
 %
 % \begin{macro}{\hook_gput_next_code:nn}
-% \begin{macro}{%
-%     \@@_gput_next_code:nn,
-%     \@@_gput_next_do:nn,
-%     \@@_gput_next_do:Nnn,
-%     \@@_clear_next:n
-%   }
 %    \begin{macrocode}
 \cs_new_protected:Npn \hook_gput_next_code:nn #1
   { \@@_normalize_hook_args:Nn \@@_gput_next_code:nn {#1} }
+%    \end{macrocode}
+%  \end{macro}
+%
+% \begin{macro}{\@@_gput_next_code:nn,
+%               \@@_gput_next_do:nn,
+%               \@@_gput_next_do:Nnn,
+%               \@@_clear_next:n}
+%    \begin{macrocode}
 \cs_new_protected:Npn \@@_gput_next_code:nn #1 #2
   {
-    \@@_declare:n {#1}
-    \hook_if_exist:nTF {#1}
-      { \@@_gput_next_do:nn {#1} {#2} }
-      { \@@_try_declaring_generic_next_hook:nn {#1} {#2} }
+    \@@_if_disabled:nTF {#1}
+      { \__kernel_msg_error:nnn { hooks } { hook-disabled } {#1} }
+      {
+        \@@_init_structure:n {#1}
+        \@@_if_usable:nTF {#1}
+          { \@@_gput_next_do:nn {#1} {#2} }
+          { \@@_try_declaring_generic_next_hook:nn {#1} {#2} }
+      }
   }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 \cs_new_protected:Npn \@@_gput_next_do:nn #1
   {
     \exp_args:Nc \@@_gput_next_do:Nnn
@@ -3814,7 +4278,11 @@
   { \cs_gset_eq:cN { @@_next~#1 } \c_empty_tl }
 %    \end{macrocode}
 %  \end{macro}
-%  \end{macro}
+%
+%
+%
+%
+%
 %
 % \subsection{Using the hook}
 %
@@ -3841,7 +4309,7 @@
 %   them causes an update, so \cs{hook_use:n} can be made expandable.
 %   This one is better not protected so that it can expand into nothing
 %   if containing no code. Also important in case of generic hooks that
-%   we do not generate a \cs{relax} as a side effect of checking for a
+%   we do not generate a \cs[no-index]{relax} as a side effect of checking for a
 %   csname. In contrast to the \TeX{} low-level
 %   \verb=\csname ...\endcsname= construct \cs{tl_if_exist:c} is
 %   careful to avoid this.
@@ -3878,7 +4346,7 @@
 % \end{macro}
 %
 % \begin{macro}[EXP]{\@@_use:wn}
-% \begin{macro}{\@@_try_file_hook:n,\@@_if_exist_use:n}
+% \begin{macro}{\@@_try_file_hook:n,\@@_if_usable_use:n}
 %   \cs{@@_use:wn} does a quick check to test if the current hook is a
 %   file hook: those need a special treatment.  If it is not, the hook
 %   does not exist.  If it is, then \cs{@@_try_file_hook:n} is called,
@@ -3888,7 +4356,7 @@
 %
 %   If it is a file-specific hook, it passes through the same
 %   normalization as during declaration, and then it is used if defined.
-%   \cs{@@_if_exist_use:n} checks if the hook exist, and calls
+%   \cs{@@_if_usable_use:n} checks if the hook exist, and calls
 %   \cs{@@_preamble_hook:n} if so, then uses the hook.
 %    \begin{macrocode}
 \cs_new:Npn \@@_use:wn #1 / #2 \s_@@_mark #3
@@ -3897,16 +4365,22 @@
       { \@@_try_file_hook:n {#3} }
       { } % Hook doesn't exist
   }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
 \cs_new_protected:Npn \@@_try_file_hook:n #1
   {
     \@@_if_file_hook:wTF #1 / / \s_@@_mark
       {
-        \exp_args:Ne \@@_if_exist_use:n
+        \exp_args:Ne \@@_if_usable_use:n
           { \exp_args:Ne \@@_file_hook_normalize:n {#1} }
       }
-      { \@@_if_exist_use:n {#1} } % file/ generic hook (e.g. file/before)
+      { \@@_if_usable_use:n {#1} } % file/ generic hook (e.g. file/before)
   }
-\cs_new_protected:Npn \@@_if_exist_use:n #1
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\cs_new_protected:Npn \@@_if_usable_use:n #1
   {
     \tl_if_exist:cT { @@~#1 }
       {
@@ -3929,7 +4403,6 @@
 %    hook name, since \cs{hook_use:n} and \cs{hook_use_once:n} are
 %    documented to not trim spaces.
 %
-%    \pho{Should this raise an error if the hook doesn't exist?}
 %    \begin{macrocode}
 \cs_new_protected:Npn \hook_use_once:n #1
   {
@@ -3953,9 +4426,10 @@
 % exist, in which case emptiness doesn't apply (though
 % \cs{tl_if_empty:N} returns false in this case).
 %
-% Hooks are a bit more complicated: they have four possible states.
+% Hooks are a bit more complicated: they have several other states as
+%    discussed in \ref{sec:existence}.
 % A hook may exist or not, and either way it may or may not be empty
-% (even a hook that doesn't exist may be non-empty).
+% (even a hook that doesn't exist may be non-empty) or may be disabled.
 %
 % A hook is said to be empty when no code was added to it, either to
 % its permanent code pool, or to its ``next'' token list.  The hook
@@ -3965,19 +4439,19 @@
 % In this case it is important that the code added by package $B$ is
 % remembered until package $A$ is loaded).
 %
-% A hook is said to exist when it was declared with \cs{hook_new:n} or
-% some variant thereof.
-%
+%    All other states can only be queried with internal tests as the
+%    different states are irrelevant for package code.
+
 % \begin{macro}[pTF]{\hook_if_empty:n}
 %   Test if a hook is empty (that is, no code was added to that hook).
 %   A \meta{hook} being empty means that all three of its
-%   \cs[no-index]{g_@@_\meta{hook}_code_prop}, its
-%   \cs[no-index]{@@_toplevel~\meta{hook}} and its
-%   \cs[no-index]{@@_next~\meta{hook}} are empty.
+%   \cs{g_@@_\meta{hook}_code_prop}, its
+%   \cs{@@_toplevel\textvisiblespace\meta{hook}} and its
+%   \cs{@@_next\textvisiblespace\meta{hook}} are empty.
 %    \begin{macrocode}
 \prg_new_conditional:Npnn \hook_if_empty:n #1 { p , T , F , TF }
   {
-    \@@_if_exist:nTF {#1}
+    \@@_if_structure_exist:nTF {#1}
       {
         \bool_lazy_and:nnTF
             { \prop_if_empty_p:c { g_@@_#1_code_prop } }
@@ -3994,8 +4468,9 @@
 %    \end{macrocode}
 % \end{macro}
 %
-% \begin{macro}[pTF]{\hook_if_exist:n}
-%   A canonical way to test if a hook exists.  A hook exists if the
+%
+% \begin{macro}[pTF]{\@@_if_usable:n}
+%   A hook is usable if the
 %   token list that stores the sorted code for that hook,
 %   \cs[no-index]{@@~\meta{hook}}, exists.  The property list
 %   \cs[no-index]{g_@@_\meta{hook}_code_prop} cannot be used here
@@ -4003,7 +4478,7 @@
 %   if such hook was already declared, or even if it will ever be
 %   (for example, in case the package that defines it isn't loaded).
 %    \begin{macrocode}
-\prg_new_conditional:Npnn \hook_if_exist:n #1 { p , T , F , TF }
+\prg_new_conditional:Npnn \@@_if_usable:n #1 { p , T , F , TF }
   {
     \tl_if_exist:cTF { @@~#1 }
       { \prg_return_true: }
@@ -4012,13 +4487,15 @@
 %    \end{macrocode}
 % \end{macro}
 %
-% \begin{macro}[pTF]{\@@_if_exist:n}
-%   An internal check if the hook has already been declared with
-%   \cs{@@_declare:n}.  This means that the hook was already used somehow
+% \begin{macro}[pTF]{\@@_if_structure_exist:n}
+%
+%    An internal check if the hook has already its basic internal
+%    structure set up with
+%   \cs{@@_init_structure:n}.  This means that the hook was already used somehow
 %   (a code chunk or rule was added to it), but it still wasn't declared
 %   with \cs{hook_new:n}.
 %    \begin{macrocode}
-\prg_new_conditional:Npnn \@@_if_exist:n #1 { p , T , F , TF }
+\prg_new_conditional:Npnn \@@_if_structure_exist:n #1 { p , T , F , TF }
   {
     \prop_if_exist:cTF { g_@@_#1_code_prop }
       { \prg_return_true: }
@@ -4026,6 +4503,22 @@
   }
 %    \end{macrocode}
 % \end{macro}
+%  
+%  
+%  
+%  \begin{macro}[pTF]{\@@_if_declared:n}
+%
+%    Internal test to check if the hook was officially declared with
+%    \cs{hook_new:n} or a variant.
+%    \begin{macrocode}
+\prg_new_conditional:Npnn \@@_if_declared:n #1 { p, T, F, TF }
+  {
+    \tl_if_exist:cTF { g_@@_#1_declared_tl }
+      { \prg_return_true: }
+      { \prg_return_false: }
+  }
+%    \end{macrocode}
+%  \end{macro}
 %
 % \begin{macro}[pTF]{\@@_if_reversed:n}
 %   An internal conditional that checks if a hook is reversed.
@@ -4045,10 +4538,10 @@
 %  \subsection{Messages}
 %
 %    \begin{macrocode}
-\msg_new:nnnn { hooks } { labels-incompatible }
+\__kernel_msg_new:nnnn { hooks } { labels-incompatible }
   {
-    Labels~`#1'~and~`#2'~are~incompatible
-    \str_if_eq:nnF {#3} {??} { ~in~hook~`#3' } .~
+    Labels~'#1'~and~'#2'~are~incompatible
+    \str_if_eq:nnF {#3} {??} { ~in~hook~'#3' } .~
     \int_compare:nNnTF {#4} = { 1 }
       { The~ code~ for~ both~ labels~ will~ be~ dropped. }
       { You~ may~ see~ errors~ later. }
@@ -4058,23 +4551,34 @@
 %    \end{macrocode}
 %    
 %    \begin{macrocode}
-\msg_new:nnnn { hooks } { exists }
-    { Hook~`#1'~ has~ already~ been~ declared. }
+\__kernel_msg_new:nnnn { hooks } { exists }
+    { Hook~'#1'~ has~ already~ been~ declared. }
     { There~ already~ exists~ a~ hook~ declaration~ with~ this~
       name.\\
       Please~ use~ a~ different~ name~ for~ your~ hook.}
 %    \end{macrocode}
 %    
+%
+%    \begin{macrocode}
+\__kernel_msg_new:nnnn { hooks } { hook-disabled }
+  { Cannot~add~code~to~disabled~hook~'#1'. }
+  {
+    The~hook~'#1'~you~tried~to~add~code~to~was~previously~disabled~
+    with~\iow_char:N\\hook_disable:n~or~\iow_char:N\\DisableHook,~so~
+    it~cannot~have~code~added~to~it.
+  }
+%    \end{macrocode}
+%
 %    \begin{macrocode}
-\msg_new:nnn { hooks } { empty-label }
+\__kernel_msg_new:nnn { hooks } { empty-label }
   {
     Empty~code~label~\msg_line_context:.~
-    Using~`\@@_currname_or_default:'~instead.
+    Using~'\@@_currname_or_default:'~instead.
   }
 %    \end{macrocode}
 %
 %    \begin{macrocode}
-\msg_new:nnn { hooks } { no-default-label }
+\__kernel_msg_new:nnn { hooks } { no-default-label }
   {
     Missing~(empty)~default~label~\msg_line_context:. \\
     This~command~was~ignored.
@@ -4082,25 +4586,25 @@
 %    \end{macrocode}
 %
 %    \begin{macrocode}
-\msg_new:nnnn { hooks } { unknown-rule }
-  { Unknown~ relationship~ `#3'~
-    between~ labels~ `#2'~ and~ `#4'~
-    \str_if_eq:nnF {#1} {??} { ~in~hook~`#1' }. ~
+\__kernel_msg_new:nnnn { hooks } { unknown-rule }
+  { Unknown~ relationship~ '#3'~
+    between~ labels~ '#2'~ and~ '#4'~
+    \str_if_eq:nnF {#1} {??} { ~in~hook~'#1' }. ~
     Perhaps~ a~ missspelling?
   }
   {
     The~ relation~ used~ not~ known~ to~ the~ system.~ Allowed~ values~ are~
-    `before'~ or~ `<',~
-    `after'~ or~ `>',~
-    `incompatible-warning',~
-    `incompatible-error',~
-    `voids'~ or~
-    `unrelated'.
+    'before'~ or~ '<',~
+    'after'~ or~ '>',~
+    'incompatible-warning',~
+    'incompatible-error',~
+    'voids'~ or~
+    'unrelated'.
   }
 %    \end{macrocode}
 %    
 %    \begin{macrocode}
-\msg_new:nnnn { hooks } { misused-top-level }
+\__kernel_msg_new:nnnn { hooks } { misused-top-level }
   {
     Illegal~\iow_char:N \\AddToHook{#1}[top-level]{...}.\\
     'top-level'~is~reserved~for~the~user's~document.
@@ -4114,16 +4618,16 @@
 %    \end{macrocode}
 %
 %    \begin{macrocode}
-\msg_new:nnn { hooks } { set-top-level }
+\__kernel_msg_new:nnn { hooks } { set-top-level }
   {
-    You~cannot~change~the~default~label~#1~`top-level'.~Illegal \\
+    You~cannot~change~the~default~label~#1~'top-level'.~Illegal \\
     \use:nn { ~ } { ~ } \iow_char:N \\#2{#3} \\
     \msg_line_context:.
   }
 %    \end{macrocode}
 %
 %    \begin{macrocode}
-\msg_new:nnn { hooks } { ddhl-deprecated }
+\__kernel_msg_new:nnn { hooks } { ddhl-deprecated }
   {
     \iow_char:N \\DeclareDefaultHookLabel~is~deprecated.\\
     Use~\iow_char:N \\SetDefaultHookLabel~instead.\\ \\
@@ -4132,26 +4636,55 @@
 %    \end{macrocode}
 %
 %    \begin{macrocode}
-\msg_new:nnn { hooks } { extra-pop-label }
+\__kernel_msg_new:nnn { hooks } { extra-pop-label }
   {
     Extra~\iow_char:N \\PopDefaultHookLabel. \\
     This~command~will~be~ignored.
   }
-\msg_new:nnn { hooks } { missing-pop-label }
+\__kernel_msg_new:nnn { hooks } { missing-pop-label }
   {
     Missing~\iow_char:N \\PopDefaultHookLabel. \\
-    The~label~`#1'~was~pushed~but~never~popped.~Something~is~wrong.
+    The~label~'#1'~was~pushed~but~never~popped.~Something~is~wrong.
   }
 %    \end{macrocode}
 %
 %    \begin{macrocode}
-\msg_new:nnn { hooks } { should-not-happen }
+\__kernel_msg_new:nnn { hooks } { should-not-happen }
   {
     ERROR!~This~should~not~happen.~#1 \\
     Please~report~at~https://github.com/latex3/latex2e.
   }
 %    \end{macrocode}
 %
+%
+%
+%    \begin{macrocode}
+\__kernel_msg_new:nnn { hooks } { provide-disabled }
+  {
+    Can't~ provide~ hook~ '#1'~ because~ it~ is~ disabled!
+  }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\__kernel_msg_new:nnnn { hooks } { provide-error }
+  {
+    Hook~'#1'~ already~ declared~ as~ a~
+    \@@_if_reversed:nTF {#1} { reversed } { normal }~ hook!
+  }
+  {
+    You~ attempted~ to~ provide~ the~ hook~'#1'~ as~ a~
+    \@@_if_reversed:nTF {#1} { normal } { reversed }~ hook,~ but~ it~
+    was~ already~ previously~ declared~ as~ a~
+    \@@_if_reversed:nTF {#1} { reversed } { normal }~ hook.~
+    A~ redeclaration~ is~ not~ possible.
+  }
+%    \end{macrocode}
+%
+%
+%
+%
+%
+%
 %  \subsection{\LaTeXe{} package interface commands}
 %
 %
@@ -4165,6 +4698,44 @@
 %    \end{macrocode}
 %  \end{macro}
 %
+%
+%
+%    \begin{macrocode}
+%<latexrelease>\IncludeInRelease{2021/06/01}%
+%<latexrelease>         {\hook_provide:n}{Providing~hooks}
+%    \end{macrocode}
+%
+%  \begin{macro}{\ProvideHook,\ProvideReversedHook,\ProvideMirroredHookPair}
+%    Providing new hooks \ldots
+% \changes{v1.0m}{2021/04/29}{Add \cs{ProvideHook} etc.}
+%    \begin{macrocode}
+\NewDocumentCommand \ProvideHook         { m }{ \hook_provide:n {#1} }
+\NewDocumentCommand \ProvideReversedHook { m }{ \hook_provide_reversed:n {#1} }
+\NewDocumentCommand \ProvideMirroredHookPair { mm }{ \hook_provide_pair:nn {#1}{#2} }
+%    \end{macrocode}
+%  \end{macro}
+%
+%
+%  \begin{macro}{\DisableHook}
+%    Disabling a (generic) hook.
+%    \begin{macrocode}
+\NewDocumentCommand \DisableHook { m }{ \hook_disable:n {#1} }
+%    \end{macrocode}
+%  \end{macro}
+%
+%    \begin{macrocode}
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\IncludeInRelease{2020/10/01}
+%<latexrelease>                 {\hook_provide:n}{Providing~hooks}
+%<latexrelease>
+%<latexrelease>\def \ProvideHook#1{}
+%<latexrelease>\def \ProvideReversedHook#1{}
+%<latexrelease>\def \ProvideMirroredHookPair#1#2{}
+%<latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%    \end{macrocode}
+%
+%
 %  \begin{macro}{\AddToHook}
 %    
 %    \begin{macrocode}
@@ -4194,6 +4765,10 @@
 % \begin{macro}{\PushDefaultHookLabel}
 % \begin{macro}{\PopDefaultHookLabel}
 % \begin{macro}{\DeclareDefaultHookLabel}
+%
+% \fmiinline{Docu task: At some point this code for this should be moved to the
+%    label section earlier and here we should keep only the interface commands.}  
+%
 % \begin{macro}{\@@_curr_name_push:n,\@@_curr_name_push_aux:n}
 % \begin{macro}{\@@_curr_name_pop:}
 % \begin{macro}{\@@_end_document_label_check:}
@@ -4217,8 +4792,11 @@
 %   the stack to support roll forward.  But in some rare cases,
 %   \pkg{latexrelease} may be loaded inside another package (notably
 %   \pkg{platexrelease}), so we'll first push the |top-level| entry:
+%   \changes{v1.0i}{2021/03/18}
+%           {Only add \texttt{top-level} if not already there.}
 %    \begin{macrocode}
-%<latexrelease>\seq_gput_right:Nn \g_@@_name_stack_seq { top-level }
+%<latexrelease>\seq_if_empty:NT \g_@@_name_stack_seq
+%<latexrelease>  { \seq_gput_right:Nn \g_@@_name_stack_seq { top-level } }
 %    \end{macrocode}
 %   then we dissect the \cs{@currnamestack}, adding \cs{@currname} to
 %   the stack:
@@ -4234,9 +4812,12 @@
 %<latexrelease>  \q_recursion_tail \q_recursion_tail
 %<latexrelease>  \q_recursion_tail \q_recursion_stop
 %    \end{macrocode}
-%   and finalle set the default label to be the \cs{@currname}:
+%   and finally set the default label to be the \cs{@currname}:
+%   \changes{v1.0i}{2021/03/18}
+%           {Remove the (empty) \enquote{top-level} from \cs{@currnamestack}.}
 %    \begin{macrocode}
 %<latexrelease>\tl_gset:Nx \g_@@_hook_curr_name_tl { \@currname }
+%<latexrelease>\seq_gpop_right:NN \g_@@_name_stack_seq \l_@@_tmpa_tl
 %    \end{macrocode}
 %
 %   Two commands keep track of the stack: when a file is input,
@@ -4248,11 +4829,11 @@
 \cs_new_protected:Npn \@@_curr_name_push_aux:n #1
   {
     \tl_if_blank:nTF {#1}
-      { \msg_error:nn { hooks } { no-default-label } }
+      { \__kernel_msg_error:nn { hooks } { no-default-label } }
       {
         \str_if_eq:nnTF {#1} { top-level }
           {
-            \msg_error:nnnnn { hooks } { set-top-level }
+            \__kernel_msg_error:nnnnn { hooks } { set-top-level }
               { to } { PushDefaultHookLabel } {#1}
           }
           {
@@ -4270,12 +4851,12 @@
   {
     \seq_gpop:NNTF \g_@@_name_stack_seq \l_@@_return_tl
       { \tl_gset_eq:NN \g_@@_hook_curr_name_tl \l_@@_return_tl }
-      { \msg_error:nn { hooks } { extra-pop-label } }
+      { \__kernel_msg_error:nn { hooks } { extra-pop-label } }
   }
 %    \end{macrocode}
 %
 %   At the end of the document we want to check if there was no
-%   \cs{@@_curr_name_push:} without a matching \cs{@@_curr_name_pop:}
+%   \cs{@@_curr_name_push:n} without a matching \cs{@@_curr_name_pop:}
 %   (not a critical error, but it might indicate that something else is
 %   not quite right):
 %    \begin{macrocode}
@@ -4285,7 +4866,7 @@
   {
     \seq_gpop:NNT \g_@@_name_stack_seq \l_@@_return_tl
       {
-        \msg_error:nnx { hooks } { missing-pop-label }
+        \__kernel_msg_error:nnx { hooks } { missing-pop-label }
           { \g_@@_hook_curr_name_tl }
         \tl_gset_eq:NN \g_@@_hook_curr_name_tl \l_@@_return_tl
         \@@_end_document_label_check:
@@ -4303,7 +4884,7 @@
   {
     \seq_if_empty:NTF \g_@@_name_stack_seq
       {
-        \msg_error:nnnnn { hooks } { set-top-level }
+        \__kernel_msg_error:nnnnn { hooks } { set-top-level }
           { for } { SetDefaultHookLabel } {#1}
       }
       { \exp_args:Nx \@@_set_default_label:n { \@@_make_name:n {#1} } }
@@ -4312,14 +4893,14 @@
   {
     \str_if_eq:nnTF {#1} { top-level }
       {
-        \msg_error:nnnnn { hooks } { set-top-level }
+        \__kernel_msg_error:nnnnn { hooks } { set-top-level }
           { to } { SetDefaultHookLabel } {#1}
       }
       { \tl_gset:Nn \g_@@_hook_curr_name_tl {#1} }
   }
 \NewDocumentCommand \DeclareDefaultHookLabel { m }
   {
-    \msg_error:nn { hooks } { ddhl-deprecated }
+    \__kernel_msg_error:nn { hooks } { ddhl-deprecated }
     \SetDefaultHookLabel {#1}
   }
 %    \end{macrocode}
@@ -4414,7 +4995,7 @@
 %  \begin{macro}{\ClearHookRule}
 %    A special setup rule that removes an existing relation.
 %    Basically {@@_rule_gclear:nnn} plus fixing the property list for debugging.
-%    \fmi{Need an L3 interface, or maybe it should get dropped?}
+%    \fmiinline{Needs perhaps an L3 interface, or maybe it should get dropped?}
 %    \begin{macrocode}
 \NewDocumentCommand \ClearHookRule { m m m }
 { \hook_gset_rule:nnnn {#1}{#2}{unrelated}{#3} }
@@ -4422,19 +5003,33 @@
 %  \end{macro}
 %
 %
-% \begin{macro}[EXP]{\IfHookExistsTF,\IfHookEmptyTF}
+% \begin{macro}[EXP]{\IfHookEmptyTF}
 %   Here we avoid the overhead of \pkg{xparse}, since \cs{IfHookEmptyTF}
 %   is used in \cs{end} (that is, every \LaTeX{} environment).  As a
 %   further optimisation, use \cs{let} rather than \cs{def} to avoid one
 %   expansion step.
 %    \begin{macrocode}
-\cs_new_eq:NN \IfHookExistsTF \hook_if_exist:nTF
 \cs_new_eq:NN \IfHookEmptyTF \hook_if_empty:nTF
 %    \end{macrocode}
 % \end{macro}
 %
+% \begin{macro}[EXP]{\IfHookExistsTF}
+%    Marked for removal and no longer documented in the doc section!
+% \phoinline{\cs{IfHookExistsTF} is used in \texttt{jlreq.cls},
+% \texttt{pxatbegshi.sty}, \texttt{pxeverysel.sty},
+% \texttt{pxeveryshi.sty}, so the public name may be an alias of the
+% internal conditional for a while.  Regardless, those packages' use for
+% \cs{IfHookExistsTF} is not really correct and can be changed.}
+%    \begin{macrocode}
+\cs_new_eq:NN \IfHookExistsTF \@@_if_usable:nTF
+%    \end{macrocode}
+% \end{macro}
+%
+%
+%
+%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %
-%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5
 %
 % \subsection{Internal commands needed elsewhere}
 %
@@ -4463,12 +5058,6 @@
 % \InternalDetectionOn
 %  \end{macro}
 %
-%    
-%    \begin{macrocode}
-\ExplSyntaxOff
-%    \end{macrocode}
-%
-%
 %    Rolling back here doesn't undefine the interface commands as they
 %    may be used in packages without rollback functionality. So we
 %    just make them do nothing which may or may not work depending on
@@ -4476,14 +5065,15 @@
 % \changes{v1.0d}{2020/10/04}{Definition \cs{AddToHookNext} was supposed
 %                             to be for \cs{AddToHook} vice versa (gh/401)}
 %    \begin{macrocode}
-%</2ekernel|latexrelease>
-%<latexrelease>\EndIncludeInRelease
+%
 %<latexrelease>\IncludeInRelease{0000/00/00}%
-%<latexrelease>                 {\NewHook}{The hook management}%
+%<latexrelease>                 {lthooks}{The~hook~management}%
+%<latexrelease>
+%<latexrelease>\def \NewHook#1{}
+%<latexrelease>\def \NewReversedHook#1{}
+%<latexrelease>\def \NewMirroredHookPair#1#2{}
 %<latexrelease>
-%<latexrelease>\def\NewHook#1{}
-%<latexrelease>\def\NewReversedHook#1{}
-%<latexrelease>\def\NewMirroredHookPair#1#2{}
+%<latexrelease>\def \DisableHook #1{}
 %<latexrelease>
 %<latexrelease>\long\def\AddToHookNext#1#2{}
 %<latexrelease>
@@ -4511,7 +5101,9 @@
 %<latexrelease>\long\def \IfHookExistsTF #1#2#3{#3}
 %<latexrelease>\long\def \IfHookEmptyTF #1#2#3{#2}
 %<latexrelease>
-%<latexrelease>\EndIncludeInRelease
+%<latexrelease>\EndModuleRelease
+\ExplSyntaxOff
+%</2ekernel|latexrelease>
 %    \end{macrocode}
 %
 %
diff --git a/Master/texmf-dist/source/latex-dev/base/ltluatex.dtx b/Master/texmf-dist/source/latex-dev/base/ltluatex.dtx
index e3fa9f93437..3b9a3377312 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltluatex.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltluatex.dtx
@@ -28,7 +28,7 @@
 \ProvidesFile{ltluatex.dtx}
 %</driver>
 %<*tex>
-[2021/01/15 v1.1s
+[2021/04/18 v1.1t
 %</tex>
 %<plain>  LuaTeX support for plain TeX (core)
 %<*tex>
@@ -1412,6 +1412,7 @@ local callbacktypes = callbacktypes or {
 % \changes{v1.1j}{2019/06/18}{make\_extensible added}
 % \changes{v1.1j}{2019/06/18}{font\_descriptor\_objnum\_provider added}
 % \changes{v1.1l}{2020/02/02}{glyph\_info added}
+% \changes{v1.1t}{2021/04/18}{input\_level\_string added}
 %    \begin{macrocode}
   define_font                     = exclusive,
   glyph_info                      = exclusive,
@@ -1419,6 +1420,7 @@ local callbacktypes = callbacktypes or {
   glyph_stream_provider           = exclusive,
   make_extensible                 = exclusive,
   font_descriptor_objnum_provider = exclusive,
+  input_level_string              = exclusive,
 %    \end{macrocode}
 % \changes{v1.0m}{2016/02/11}{pdf\_stream\_filter\_callback removed}
 %    \begin{macrocode}
@@ -1477,7 +1479,7 @@ end
 %     functions in inverse order.
 %   \item[exclusive] is for functions with more complex signatures; functions in
 %     this type of callback are \emph{not} combined: An error is raised if
-%     a second callback is registered..
+%     a second callback is registered.
 % \end{description}
 %
 % Handler for |data| callbacks.
diff --git a/Master/texmf-dist/source/latex-dev/base/ltmath.dtx b/Master/texmf-dist/source/latex-dev/base/ltmath.dtx
index ca90e1980d2..aadb96fb023 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltmath.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltmath.dtx
@@ -38,7 +38,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltmath.dtx}
-              [2020/12/05 v1.2h LaTeX Kernel (Math Setup)]
+              [2021/04/20 v1.2i LaTeX Kernel (Math Setup)]
 % \iffalse
 %</driver>
 %
@@ -961,11 +961,12 @@
 % \end{macro}
 %
 % \begin{macro}{\@eqncr}
+% \changes{v1.2i}{2021/04/20}{Use \cs{protected} for \cs{\bslash} variant (gh/548)}
 % \begin{macro}{\@xeqncr}
 % \begin{macro}{\@yeqncr}
 % \changes{v1.0y}{1995/10/16}{(DPC) Use \cs{@testopt} /1911}
 %    \begin{macrocode}
-\def\@eqncr{%
+\protected\def\@eqncr{%
    {\ifnum0=`}\fi
    \@ifstar{%
       \global\@eqpen\@M\@yeqncr
@@ -1033,8 +1034,9 @@
 \let\@seqncr=\@eqncr
 %    \end{macrocode}
 %
+% \changes{v1.2i}{2021/04/20}{Use \cs{protected} for \cs{\bslash} variant (gh/548)}
 %    \begin{macrocode}
-\@namedef{eqnarray*}{\def\@eqncr{\nonumber\@seqncr}\eqnarray}
+\@namedef{eqnarray*}{\protected\def\@eqncr{\nonumber\@seqncr}\eqnarray}
 %    \end{macrocode}
 %
 %    \begin{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/base/ltmiscen.dtx b/Master/texmf-dist/source/latex-dev/base/ltmiscen.dtx
index 939bd51a2da..8bae3f9bfa3 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltmiscen.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltmiscen.dtx
@@ -400,7 +400,7 @@
 %    \begin{macrocode}
 %</2ekernel>
 %<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2021/05/01}%
+%<latexrelease>\IncludeInRelease{2021/06/01}%
 %<latexrelease>                 {\@kernel@before@enddocument}{kernel before hook}%
 \def\@kernel@before@enddocument{\par}
 %</2ekernel|latexrelease>
diff --git a/Master/texmf-dist/source/latex-dev/base/ltoutenc.dtx b/Master/texmf-dist/source/latex-dev/base/ltoutenc.dtx
index 73146428c0d..eb2ecd1e537 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltoutenc.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltoutenc.dtx
@@ -37,14 +37,14 @@
 %<TS1>\ProvidesFile{ts1enc.def}[2001/06/05 v3.0e (jk/car/fm)
 %<TU>\ProvidesFile{tuenc.def}
 %<package>\ProvidesPackage{fontenc}
-%<OT1|T1|OMS|OML|OT4|TU|package> [2021/02/19 v2.0u
+%<OT1|T1|OMS|OML|OT4|TU|package> [2021/04/29 v2.0v
 %<OT1|T1|OMS|OML|OT4|TS1|TU>      Standard LaTeX file]
 %<package>                        Standard LaTeX package]
 %
 %<*driver>
 % \fi
 \ProvidesFile{ltoutenc.dtx}
-             [2021/02/19 v2.0u LaTeX Kernel (font encodings)]
+             [2021/04/29 v2.0v LaTeX Kernel (font encodings)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltoutenc.dtx}
@@ -3468,8 +3468,19 @@
 \DeclareUnicodeComposite{\v}             {o}{"01D2}
 \DeclareUnicodeComposite{\v}             {U}{"01D3}
 \DeclareUnicodeComposite{\v}             {u}{"01D4}
+%    \end{macrocode}
+%
+% \changes{v2.0v}{2021/04/29}{Add composites for
+%      \texttt{\protect\string\ae/\protect\string\AE/\ae/\AE} (gh/552)}
+%    \begin{macrocode}
+\DeclareUnicodeComposite{\'}             \AE{"01FC}
+\DeclareUnicodeComposite{\'}             {Æ}{"01FC}
+\DeclareUnicodeComposite{\'}             \ae{"01FD}
+\DeclareUnicodeComposite{\'}             {æ}{"01FD}
 \DeclareUnicodeComposite{\=}             \AE{"01E2}
+\DeclareUnicodeComposite{\=}             {Æ}{"01E2}
 \DeclareUnicodeComposite{\=}             \ae{"01E3}
+\DeclareUnicodeComposite{\=}             {æ}{"01E3}
 \DeclareUnicodeComposite{\v}             {G}{"01E6}
 \DeclareUnicodeComposite{\v}             {g}{"01E7}
 \DeclareUnicodeComposite{\v}             {K}{"01E8}
diff --git a/Master/texmf-dist/source/latex-dev/base/ltpar.dtx b/Master/texmf-dist/source/latex-dev/base/ltpar.dtx
index f4f3d5e63fc..969954be0a7 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltpar.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltpar.dtx
@@ -33,7 +33,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltpar.dtx}
-             [1995/04/29 v1.1c LaTeX Kernel (paragraphs)]
+             [2021/04/13 v1.1c LaTeX Kernel (paragraphs)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltpar.dtx}
@@ -67,9 +67,11 @@
 % |\par| and |\everypar| when ever their function needs to be
 % changed for a long time.
 %
-% \StopEventually{}
-%
-% \subsection{Implementation}
+% This file here describes the interfaces that have been in the kernel
+% forever, used to implement the scenarios described below. They
+% remain valid but are now augmented in the next file
+% (\texttt{ltpara.dtx}) to add hooks to paragraphs. At some point we
+% will consolidate the two files further.
 %
 %
 % There are two situations in which |\par| may be changed:
@@ -93,6 +95,12 @@
 %       \end{itemize}
 % \end{itemize}
 %
+%
+% \StopEventually{}
+%
+% \subsection{Implementation}
+%
+%
 % \DescribeMacro{\@setpar}
 % To permit the proper interaction of these two situations, long-term
 % changes are made by the |\@setpar{|\meta{VAL}|}| command.
diff --git a/Master/texmf-dist/source/latex-dev/base/ltpara.dtx b/Master/texmf-dist/source/latex-dev/base/ltpara.dtx
index 1a3df95a6e2..ad503b68e25 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltpara.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltpara.dtx
@@ -11,11 +11,11 @@
 %    https://www.latex-project.org/lppl.txt
 %
 %
-%%% From File: lthooks.dtx
+%%% From File: ltpara.dtx
 %
 %    \begin{macrocode}
-\def\ltparaversion{v1.0d}
-\def\ltparadate{2021/02/18}
+\def\ltparaversion{v1.0f}
+\def\ltparadate{2021/04/16}
 %    \end{macrocode}
 %<*driver>
 \documentclass{l3doc}
@@ -302,13 +302,14 @@
 %      \cs{noindent}).
 %
 %      The indentation box to be typeset is available to the hook as
-%      \cs{IndentationBox} and its automatic placement (after the hook is
-%      executed) can be prevented through \cs{SuppressIndentationBox}.
+%      \cs{IndentBox} and its automatic placement (after the hook is
+%      executed) can be prevented through \cs{OmitIndent}.
+%      More precisely \cs{OmitIndent} voids the box.
 %
-%      If not suppressed, then the indentation is typeset directly
+%      The indentation box is then typeset directly
 %      after the hook execution by something equivalent to
-%      \cs{box}\cs{IndentationBox} followed by the current content of
-%      the token register \cs{everypar} as it is available to the
+%      \cs{box}\cs{IndentBox} followed by the current content of
+%      the token register \cs{everypar} that it is available to the
 %      kernel or to packages (that run some legacy code).
 %
 %      One has to be careful not to add any code to the hook that
@@ -375,7 +376,7 @@
 %    \item[\cs{@kernel@before@para@before}]
 %       For future extensions, not currently used by the kernel.
 %
-
+%
 %    \item[\cs{@kernel@after@para@after}]
 %       For future extensions, not currently used by the kernel.
 %
@@ -437,26 +438,67 @@
 %    Spring release!
 % \end{quote}
 %
-% \begin{function}{\SuppressIndentationBox,\para_suppress_indentation:}
+% \begin{function}{\OmitIndent,\para_omit_indent:}
 %    Inside the \hook{para/begin} hook one can use this command to
 %    suppress the indentation box at the start of the
 %    paragraph. (Technically it is possible to use this command
 %    outside the hook as well, but this should not be relied upon.)
 %    The box itself remains available for use.
 %
-%    The \pkg{expl3} name for the function is \cs{para_suppress_indentation:}.
+%    The \pkg{expl3} name for the function is \cs{para_omit_indent:}.
 % \end{function}
 %
-% \begin{variable}{\IndentationBox,\g_para_indentation_box}
+% \begin{variable}{\IndentBox,\g_para_indent_box}
 %    The box register holding the indentation box for the paragraph is
 %    available for inspection (or changes) inside hooks. It remains
-%    available even if the \cs{SuppressIndentationBox} command was
+%    available even if the \cs{OmitIndent} command was
 %    used; in that case it  will just not be automatically placed.
 %
-%    The \pkg{expl3} name for the box register is \cs{g_para_indentation_box}.
+%    The \pkg{expl3} name for the box register is \cs{g_para_indent_box}.
 % \end{variable}
 %
 %
+% \begin{function}{\RawIndent,\para_raw_indent:,
+%                  \RawNoindent,\para_raw_noindent:,
+%                  \RawParEnd,\para_raw_end:}
+% \begin{syntax}
+%   \cs{RawIndent}   \textit{hmode material} \cs{RawParEnd}
+%   \cs{RawNoindent} \textit{hmode material} \cs{RawParEnd}
+% \end{syntax}
+%
+%    The commands \cs{RawIndent} and \cs{RawNoindent} are not meant
+%    for normal paragraph building (where the result is a textual
+%    paragraph in the the traditional meaning of the word), but for
+%    special cases where \TeX{}'s low-level algorithm is used to
+%    achieve special effects, but where the result is not a
+%    \enquote{paragraph}.
+%
+%    They are called \enquote{raw}, because they bypass \LaTeX{}'s
+%    hook mechanism for paragraphs and simply invoke the low-level
+%    \TeX{} algorithm.  I.e., they are like the original \TeX{}
+%    primitives \cs{indent} and \cs{noindent} (that is they execute no
+%    hooks other than \cs{everypar}) except that they can only be used
+%    in vertical mode and generate an error if found elsewhere.
+%
+%    To avoid issues a paragraph started by them should always be
+%    ended by \cs{RawParEnd}\footnote{Technical note for those who
+%    know their \textit{\TeX book\/}: the \cs{RawParEnd} comand
+%    invokes the original \TeX{} engine definition of \cs{par} that
+%    (soley) triggers the paragraph builder in \TeX{} when found
+%    inside unrestricted horizontal mode and does nothing in other
+%    processing modes.}
+%    and not by \cs{par} (or a blank line), because the latter will execute
+%    hooks which then have no counterpart at the beginning of the
+%    paragraph. It is the responsibility of the programmer to make
+%    sure that they are properly paired. This also means that one
+%    should not put arbitrary user content between these commands if
+%    that content could contain stray \cs{par}s.
+%
+%    The \pkg{expl3} names for the functions are
+%    \cs{para_raw_indent:}, \cs{para_raw_indent:} and
+%    \cs{para_raw_end:}.
+% \end{function}
+%
 %
 %
 % \subsection{Examples}
@@ -574,21 +616,70 @@
 %    in blue.
 %
 %
+%
+% \subsection{Some technical notes}
+%
+%    The code tries hard to be transparent for package code, but of
+%    course any change means that there is a potential for breaking
+%    other code. So in section we collect a few cases that may be of
+%    importance if low-level code is dealing with paragraphs that are
+%    now behaving slightly differently. The notes are from issues we
+%    observed and will probably grow over time.
+%
+% \subsubsection{Glue items between paragraphs (found with \pkg{fancypar})}
+%
+%    In the past \LaTeX{} placed two glue items between two
+%    consecutive paragraph, e.g.,
+%\begin{verbatim}
+%   text1 \par text2 \par
+%\end{verbatim}
+%   would show something like
+%\begin{verbatim}
+% \glue(\parskip) 0.0 plus 1.0
+% \glue(\baselineskip) 5.16669
+%\end{verbatim}
+%   but now there is anothe \cs{parskip} glue (that is always 0pt):
+%\begin{verbatim}
+% \glue(\parskip) 0.0 plus 1.0
+% \glue(\parskip) 0.0
+% \glue(\baselineskip) 5.16669
+%\end{verbatim}
+%    The reason is that we generate a \enquote{fake}'' paragraph to
+%    gain control and safely add the early hooks, but this generates
+%    an additional glue item. That item doesn't contribute anything
+%    vertically but ifsomebody writes code the unravels a constructed
+%    list using \cs{lastbox}, \cs{unskip} and \cs{unpenalty} then the
+%    code has to remove one additional glue item  or else will fail.
+
+%
+% ^^A \subsubsection{}
+%
+%
+%
+% ^^A \subsubsection{}
+%
+%
+%
+%
+%
+%
 % \StopEventually{\setlength\IndexMin{200pt}  \PrintIndex  }
 %
 %
 % \section{The Implementation}
 %
 %    \begin{macrocode}
-%<*2ekernel>
+%<@@=para>
 %    \end{macrocode}
 %
+%
 %    \begin{macrocode}
-%<@@=para>
+%<*2ekernel|latexrelease>
 \ExplSyntaxOn
+%<latexrelease>\NewModuleRelease{2021/06/01}{ltpara}
+%<latexrelease>                 {Paragraph~handling~and~hooks}
 %    \end{macrocode}
-
-
+%
 %
 %
 % \subsection{Providing hooks for paragraphs}
@@ -641,10 +732,10 @@
 \tl_gset:Nn \g_@@_standard_everypar_tl {
 %    \end{macrocode}
 %    First we remove the indentation box and store it in
-%    \cs{g_para_indentation_box}. If there was none because the paragraph
+%    \cs{g_para_indent_box}. If there was none because the paragraph
 %    was started by \cs{noindent} the box register will be void.
 %    \begin{macrocode}
-  \box_gset_to_last:N \g_para_indentation_box
+  \box_gset_to_last:N \g_para_indent_box
 %    \end{macrocode}
 %
 %    This will make the newly started horizontal list empty, so if we
@@ -683,13 +774,6 @@
 %    case there are nested paragraphs coming up.
 %    \begin{macrocode}
   \tex_everypar:D{\g_@@_standard_everypar_tl}
-%  \showthe\tex_everypar:D
-%    \end{macrocode}
-%    Then we set up \cs{@@_handle_indent:} to reinsert the indentation
-%    box later. This can be undone via \cs{SuppressIndentationBox}
-%    inside the hook(s).
-%    \begin{macrocode}
-  \cs_set_eq:NN \@@_handle_indent: \@@_add_indentation_box:
 %    \end{macrocode}
 %
 %    This is followed by executing the kernel and the public hook. The
@@ -710,7 +794,7 @@
 %    we add that later, and indirectly.
 %    \begin{macrocode}
   \@@_handle_indent:
-% \the \everypar           % <--- done differently
+% \the \everypar           % <--- done differently below
 }
 %    \end{macrocode}
 %  \end{macro}
@@ -782,40 +866,38 @@
 %  \end{macro}
 %
 %
-%  \begin{macro}{\g_para_indentation_box}
+%  \begin{macro}{\g_para_indent_box}
 %    For managing the indentation we need to provide a public
 %    accessible box register
 %    \begin{macrocode}
-\box_new:N \g_para_indentation_box
+\box_new:N \g_para_indent_box
 %    \end{macrocode}
 %  \end{macro}
 
-%  \begin{macro}{\@@_handle_indent:,\@@_add_indentation_box:}
-%    Adding (typesetting) the indent box is straight forward, the
-%    default action for is \cs{@@_handle_indent:} is
-%    \cs{@@_add_indentation_box:}.
+%  \begin{macro}{\@@_handle_indent:}
+%    Adding (typesetting) the indent box is straight forward.
+%    If it was emptied before it does nothing.
 %    \begin{macrocode}
-\cs_new:Npn \@@_add_indentation_box: {
-  \box_use_drop:N \g_para_indentation_box
+\cs_new:Npn \@@_handle_indent: {
+  \box_use_drop:N \g_para_indent_box
 }
-\cs_new_eq:NN \@@_handle_indent: \@@_add_indentation_box:
 %    \end{macrocode}
-%     The declaration \cs{para_suppress_indentation:} (or
-%    \cs{SuppressIndentationBox}) changes that to do nothing.
+%     The declaration \cs{para_omit_indent:} (or
+%    \cs{OmitIndent}) changes that to do nothing.
 %    \begin{macrocode}
-\cs_new:Npn \para_suppress_indentation: {
-  \cs_set_eq:NN \@@_handle_indent: \prg_do_nothing:
+\cs_new:Npn \para_omit_indent: {
+  \box_gclear:N \g_para_indent_box
 }
 %    \end{macrocode}
 %  \end{macro}
 %
 %
-%  \begin{macro}{\IndentationBox,\SuppressIndentationBox}
+%  \begin{macro}{\IndentBox,\OmitIndent}
 %    The \LaTeXe{} names for the indentation box and for suppressing it
 %    for use in the \hook{para/begin} hook.
 %    \begin{macrocode}
-\cs_set_eq:NN \IndentationBox \g_para_indentation_box
-\cs_set_eq:NN \SuppressIndentationBox \para_suppress_indentation:
+\cs_set_eq:NN \IndentBox \g_para_indent_box
+\cs_set_eq:NN \OmitIndent \para_omit_indent:
 %    \end{macrocode}
 %  \end{macro}
 %
@@ -979,6 +1061,67 @@
 %    \end{macrocode}
 %  \end{macro}
 %
+%
+%
+%
+%  \begin{macro}{\para_raw_indent:,
+%                \para_raw_noindent:,
+%                \para_raw_end:}
+%
+%    The commands \cs{para_raw_indent:} and \cs{para_raw_noindent:}
+%    are like the primitives \cs{indent} and \cs{noindent} except that
+%    they can only be used in vertical mode.
+%
+%    To avoid issues a paragraph started by them should always be
+%    ended by \cs{para_raw_end:} and not by \cs{para_end:} or
+%    \cs{par} as the latter will execute hooks which then have no
+%    counterpart at the beginning of the paragraph. It is the
+%    responsibility of the programmer to make sure that they are
+%    properly paired.
+%    \begin{macrocode}
+\cs_new:Npn \para_raw_indent: {
+  \mode_if_vertical:TF
+       {
+         \tex_everypar:D {
+           \box_gset_to_last:N \g_para_indent_box
+           \tex_everypar:D { \g_@@_standard_everypar_tl }
+           \@@_handle_indent:
+           \the\everypar }
+       }
+       { \__kernel_msg_error:nn {para}{raw} }
+  \tex_indent:D
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\cs_new:Npn \para_raw_noindent: {
+  \mode_if_vertical:TF
+       {
+         \tex_everypar:D {
+           \tex_everypar:D { \g_@@_standard_everypar_tl }
+           \the\everypar }
+       }
+       { \__kernel_msg_error:nn {para}{raw} }
+  \tex_noindent:D
+}
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\cs_new_eq:NN \para_raw_end: \tex_par:D
+%    \end{macrocode}
+%  \end{macro}
+%
+%
+%  \begin{macro}{\RawIndent,\RawNoIndent,\RawParEnd}
+%    The \LaTeXe{} names for starting and ending a paragraph without adding any hooks.
+%    \begin{macrocode}
+\cs_set_eq:NN \RawIndent   \para_raw_indent:
+\cs_set_eq:NN \RawNoindent \para_raw_noindent:
+\cs_set_eq:NN \RawParEnd   \para_raw_end:
+%    \end{macrocode}
+%  \end{macro}
+%
+%
 %    This ends the \texttt{para} module code.
 %    \begin{macrocode}
 %<@@=>
@@ -1010,7 +1153,10 @@
 %
 %   \subsection{The error messages}
 %
-%    Well, one really, first argument is the hook name second the mode
+%    This one is used when we detect that some hook code has changed
+%    the mode where it shouldn't, e.g., by starting or ending a
+%    paragraph.
+%    The first argument is the hook name second the mode
 %    it should have stayed in but didn't.
 %    \begin{macrocode}
 \__kernel_msg_new:nnnn {para} {mode}
@@ -1026,72 +1172,43 @@
   }
 %    \end{macrocode}
 %
+%    And here is one used in the \enquote{raw} commands when they are
+%    used outside of vertical mode. 
 %    \begin{macrocode}
-\ExplSyntaxOff
-%    \end{macrocode}
-%
-%  \subsection{Kernel corrections}
-%
-%    These corrections/changes are already part of the 2021/05
-%    release, i.e., but for testing with older releases they have been
-%    included here for now. So this section will vanish soon.
-%
-%
-%    Marginpar boxes are missing a final internal \cs{par}.
-%    \begin{macrocode}
-\IfFormatAtLeastTF{2021/05/01}{}
-{
-\long\def \@savemarbox #1#2{%
-  \global\setbox #1%
-    \color@vbox
-      \vtop{%
-        \hsize\marginparwidth
-        \@parboxrestore
-        \@marginparreset
-        #2\par                    % <-- needed
-        \@minipagefalse
-        \outer@nobreak
-        }%
-    \color@endbox
-}
+\__kernel_msg_new:nnnn {para} {raw}
+  {
+     Paragraph started while not in vertical mode.
+  }
+  {
+    Starting a paragraph with \RawIndent or \RawNoindent
+    (or \para_raw_indent: or \para_raw_noindent:) is only
+    allowed if LaTeX is in vertical mode.
+  }
 %    \end{macrocode}
-%
-%    Two sample definitions for the kernel hooks to help a bit with
-%    tracing.
+
+
 %    \begin{macrocode}
-\newcounter{paracnt}
-\def\@kernel@before@para@begin{%
-  \stepcounter{paracnt}%
-  \typeout{PARA: \arabic{paracnt} start
-    (\@currenvir\space level\on@line)}%
-}
-\def\@kernel@after@para@end  {%
-  \typeout{PARA: \arabic{paracnt} end \space\space
-    (\@currenvir\space level\on@line)}%
-  \addtocounter{paracnt}{-1}%
-}
-%    \end{macrocode}
-%
 %
-%    The next lines belong in the kernel and just make sure that  we
-%    avoid the these days unnecessary optimization that \TeX{} doesn't
-%    call on \cs{par} if a vertical box ends in hmode. Instead \TeX{}
-%    directly calls the par builder in that case :-(.
-%    \begin{macrocode}
-\let\color@begingroup\begingroup
-\def\color@endgroup{\endgraf\endgroup}
-\def\color@setgroup{\color@begingroup}  % \def\color@setgroup{\color@begingroup\set@color}
-\def\color@hbox{\hbox\bgroup\color@begingroup}
-\def\color@vbox{\vbox\bgroup\color@begingroup}
-\def\color@endbox{\color@endgroup\egroup}
-}
+%<latexrelease>\IncludeInRelease{0000/00/00}%
+%<latexrelease>                 {ltpara}{Undo~hooks~for~paragraphs}
+%<latexrelease>
+%<latexrelease>\let \OmitIndent  \@undefined
+%<latexrelease>\let \IndentBox   \@undefined
+%<latexrelease>\let \RawIndent   \@undefined
+%<latexrelease>\let \RawNoindent \@undefined
+%<latexrelease>\let \RawParEnd   \@undefined
+%<latexrelease>
+%<latexrelease>\cs_set_eq:NN \par     \tex_par:D
+%<latexrelease>\cs_set_eq:NN \@@par   \tex_par:D
+%<latexrelease>\cs_set_eq:NN \endgraf \tex_par:D
+%<latexrelease>  
+%<latexrelease>\EndModuleRelease
+\ExplSyntaxOff
+%</2ekernel|latexrelease>
 %    \end{macrocode}
 %
 %
 %
-%    \begin{macrocode}
-%<*2ekernel>
-%    \end{macrocode}
 %
 %
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
@@ -1099,61 +1216,3 @@
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %
 
-%%%% unused as hok was dropped
-
-% \subsubsection{Put the first word of each paragraph in an \cs{fbox} and append
-%    a \P{} sign at the end of the paragraph}
-%
-%    We make the assumption that the first word ends in a space so
-%    that we can grab it easily (which
-%    is of course not quite right). So here is the code for that.
-%\begin{verbatim}
-%  \def\firstwordboxed#1 {\fbox{#1} }
-%\end{verbatim}
-%    Installing that is then just a matter of putting it into the right
-%    hook. Since we don't want to box the indentation (or what comes
-%    from \cs{everypar} we shouldn't use \hook{para/begin} but
-%    \hook{para/textbegin}.
-%    Adding the \P{} is equally simple.
-%\begin{verbatim}
-%  \AddToHook{para/textbegin}{\firstwordboxed}
-%  \AddToHook{para/end}{\P}
-%\end{verbatim}
-%    While this will work more or less flawless (if you accept that it
-%    will pick up any punctuation after the first word), it will fail
-%    in at least two cases.
-%    \begin{itemize}
-%    \item Single word paragraphs ending with \cs{par} instead of an
-%    empty line will blow up because the \cs{par} will be picked up as
-%    part of the argument and error as our \cs{firstwordboxed} doesn't
-%    accept a \cs{par} not being long. That is actually good, because
-%    picking it up would be worse: it would get ignored inside
-%    \cs{fbox} and so the paragraph would be combined with the next
-%    (or worse).
-%
-%    \item The second problem is, of course, that sticking it into
-%    every \hook{para/textbegin} means it get applied to places like
-%    \cs{section} which is not really what you want. So some more
-%    elaborate mechanism would be necessary---a task for another rainy
-%    day.
-%    \end{itemize}
-%
-%    There is one other point to note here. The \cs{firstwordboxed} is
-%    expected to scan ahead. So can that kind of code be placed into a
-%    hook? The answer is a kind of yes and no.
-
-%    Hooks can receive code from different places, but obviously only
-%    one chunk of code can do some scanning ahead, the one that comes
-%    last. Any hook code in a different position would see any
-%    following code from later chunks as part of the scanning which
-%    may or may not be a problem. In fact, even in our simple example,
-%    the argument picked up by \cs{firstwordboxed} isn't really the
-%    first word of the paragraph. It is that but in front of it there
-%    is also the code responsible for running
-%    \verb=\AddTohookNext{para/textbegin}=. As long as this is not
-%    doing anything harmful it doesn't hurt in this case, but it
-%    clearly shows that this example is not as  simple as it
-%    claims to be and on the whole we have to conclude that hooks
-%    aren't really meant to do such scanning or at least not without a
-%    lot of precaution.
-%
diff --git a/Master/texmf-dist/source/latex-dev/base/ltpictur.dtx b/Master/texmf-dist/source/latex-dev/base/ltpictur.dtx
index b958d43760c..ae8b58995da 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltpictur.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltpictur.dtx
@@ -32,7 +32,7 @@
 %<*driver>
 % \fi
       \ProvidesFile{ltpictur.dtx}
-                      [2020/12/05 v1.2a LaTeX Kernel (Picture Mode)]
+                      [2021/04/20 v1.2b LaTeX Kernel (Picture Mode)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltpictur.dtx}
@@ -454,9 +454,10 @@
 % \end{macro}
 %
 % \begin{macro}{\@stackcr}
+% \changes{v1.2b}{2021/04/20}{Use \cs{protected} for \cs{\bslash} variant (gh/548)}
 % \begin{macro}{\@ixstackcr}
 %    \begin{macrocode}
-\def\@stackcr{\@ifstar\@ixstackcr\@ixstackcr}
+\protected\def\@stackcr{\@ifstar\@ixstackcr\@ixstackcr}
 \def\@ixstackcr{\@ifnextchar[\@istackcr{\cr\ignorespaces}}
 %    \end{macrocode}
 % \end{macro}
diff --git a/Master/texmf-dist/source/latex-dev/base/ltplain.dtx b/Master/texmf-dist/source/latex-dev/base/ltplain.dtx
index fa53cc17ece..e0fbcecf1b6 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltplain.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltplain.dtx
@@ -32,7 +32,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltplain.dtx}
-             [2020/11/26 v2.3d LaTeX Kernel (Plain TeX)]
+             [2021/04/18 v2.3f LaTeX Kernel (Plain TeX)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltplain.dtx}
@@ -823,6 +823,28 @@
 %    \end{macrocode}
 % \end{macro}
 %
+%
+%
+%  \begin{macro}{\@inputcheck}
+%  \begin{macro}{\@unused}
+%    Allocate read stream for testing and output stream that is never open an
+%    thus writes to the terminal.
+% \changes{v1.0l}{1994/11/07}
+%      {move here from ltdefns, remove duplicate \cs{@mainaux}}
+% \changes{v2.3e}{2021/03/26}{Allocate \cs{@inputcheck} and
+%    \cs{@unused} early so that they are before expl3 allocates
+%    more streams (gh/538)}
+%    \begin{macrocode}
+\newread\@inputcheck
+\newwrite\@unused
+%    \end{macrocode}
+%  \end{macro}
+%  \end{macro}
+%
+%
+%
+%
+%
 % \begin{macro}{\maxdimen}
 % \begin{macro}{\hideskip}
 % Here are some examples of allocation.
@@ -898,6 +920,37 @@
 %    \end{macrocode}
 % \tracingcommands=0
 % \tracingrestores=0
+%    \end{macrocode}
+%
+% \begin{macro}{\tracingstacklevels}
+%   For Lua\TeX, the \cs{tracingstacklevels} functionality was
+%   implemented as a callback, so here we just define the count register
+%   to hold the value of the parameter.
+%    \begin{macrocode}
+%</2ekernel>
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2021/06/01}{\tracingstacklevels}%
+%<latexrelease>                 {tracingstacklevels}%
+\ifx\directlua\@undefined
+  % \tracingstacklevels=0 % added in 2021
+\else
+  \newcount\tracingstacklevels
+  % Code for \tracingstacklevels defined in ltfinal.dtx
+\fi
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>
+%<latexrelease>\IncludeInRelease{0000/00/00}{\tracingstacklevels}%
+%<latexrelease>                 {tracingstacklevels}%
+%<latexrelease>\ifx\directlua\@undefined
+%<latexrelease>\else
+%<latexrelease>  \let\tracingstacklevels\@undefined
+%<latexrelease>\fi
+%<latexrelease>\EndIncludeInRelease
+%</2ekernel|latexrelease>
+%<*2ekernel>
+%    \end{macrocode}
+% \end{macro}
+%
 % \language=0
 %    \begin{macrocode}
 \uchyph=1
@@ -1482,42 +1535,68 @@
 % \changes{v2.0b}{2012/01/20}{etex tracing if available}
 % \changes{v2.0d}{2015/02/20}{Spell commands correctly :-)}
 % \changes{v2.0g}{2015/03/10}{Reorganize to be less noisy}
+% \changes{v2.3f}{2021/04/18}{Drop pre-$\varepsilon$-\TeX{} support}
+% \changes{v2.3f}{2021/04/18}
+%                {Add \cs{tracingstacklevels} and \cs{tracinglostchars}=3}
 %    \begin{macrocode}
-%<latexrelease>\IncludeInRelease{2015/01/01}{\loggingall}{etex tracing}%
+%<latexrelease>\IncludeInRelease{2021/06/01}{\loggingall}
+%<latexrelease>                 {\tracingstacklevels and \tracinglostchars=3}%
 %<*2ekernel|latexrelease>
-\ifx\tracingscantokens\@undefined
-\gdef\loggingall{%
+\edef\loggingall{%
   \tracingstats\tw@
   \tracingpages\@ne
-  \tracinglostchars\@ne
-  \tracingparagraphs\@ne
-  \errorcontextlines\maxdimen
-  \loggingoutput
-  \tracingmacros\tw@
-  \tracingcommands\tw@
-  \tracingrestores\@ne
-  }%
-\else
-\gdef\loggingall{%
-  \tracingstats\tw@
-  \tracingpages\@ne
-  \tracinglostchars\tw@
+  \tracinglostchars\thr@@
   \tracingparagraphs\@ne
   \tracinggroups\@ne
   \tracingifs\@ne
   \tracingscantokens\@ne
   \tracingnesting\@ne
   \errorcontextlines\maxdimen
-  \loggingoutput
+  \ifdefined\tracingstacklevels \tracingstacklevels\maxdimen \fi
+  \noexpand \loggingoutput
   \tracingmacros\tw@
   \tracingcommands\thr@@
   \tracingrestores\@ne
   \tracingassigns\@ne
 }%
-\fi
-\gdef\tracingall{\showoverfull\loggingall}
+\def\tracingall{\showoverfull\loggingall}
 %</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
+%<latexrelease>
+%<latexrelease>\IncludeInRelease{2015/01/01}{\loggingall}{etex tracing}%
+%<latexrelease>\ifx\tracingscantokens\@undefined
+%<latexrelease>\gdef\loggingall{%
+%<latexrelease>  \tracingstats\tw@
+%<latexrelease>  \tracingpages\@ne
+%<latexrelease>  \tracinglostchars\@ne
+%<latexrelease>  \tracingparagraphs\@ne
+%<latexrelease>  \errorcontextlines\maxdimen
+%<latexrelease>  \loggingoutput
+%<latexrelease>  \tracingmacros\tw@
+%<latexrelease>  \tracingcommands\tw@
+%<latexrelease>  \tracingrestores\@ne
+%<latexrelease>  }%
+%<latexrelease>\else
+%<latexrelease>\gdef\loggingall{%
+%<latexrelease>  \tracingstats\tw@
+%<latexrelease>  \tracingpages\@ne
+%<latexrelease>  \tracinglostchars\tw@
+%<latexrelease>  \tracingparagraphs\@ne
+%<latexrelease>  \tracinggroups\@ne
+%<latexrelease>  \tracingifs\@ne
+%<latexrelease>  \tracingscantokens\@ne
+%<latexrelease>  \tracingnesting\@ne
+%<latexrelease>  \errorcontextlines\maxdimen
+%<latexrelease>  \loggingoutput
+%<latexrelease>  \tracingmacros\tw@
+%<latexrelease>  \tracingcommands\thr@@
+%<latexrelease>  \tracingrestores\@ne
+%<latexrelease>  \tracingassigns\@ne
+%<latexrelease>}%
+%<latexrelease>\fi
+%<latexrelease>\gdef\tracingall{\showoverfull\loggingall}
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>
 %<latexrelease>\IncludeInRelease{0000/00/00}{\loggingall}{etex tracing}%
 %<latexrelease>\gdef\loggingall{\tracingcommands\tw@\tracingstats\tw@
 %<latexrelease>  \tracingpages\@ne\tracinglostchars\@ne
@@ -1532,29 +1611,14 @@
 %
 % \begin{macro}{\tracingnone}
 % \changes{v2.0g}{2015/03/10}{macro added}
-% \begin{macro}{\hideoutput}
-% \changes{v2.0g}{2015/03/10}{macro added}
+% \changes{v2.3f}{2021/04/18}{Drop pre-$\varepsilon$-\TeX{} support}
+% \changes{v2.3f}{2021/04/18}
+%                {Add \cs{tracingstacklevels} and \cs{tracinglostchars}=3}
 %    \begin{macrocode}
 %<latexrelease>\IncludeInRelease{2015/01/01}{\tracingnone}%
 %<latexrelease>                             {turn off etex tracing}%
 %<*2ekernel|latexrelease>
-\ifx\tracingscantokens\@undefined
-\def\tracingnone{%
-  \tracingonline\z@
-  \tracingcommands\z@
-  \showboxdepth\m@ne
-  \showboxbreadth\m@ne
-  \tracingoutput\z@
-  \errorcontextlines\m@ne
-  \tracingrestores\z@
-  \tracingparagraphs\z@
-  \tracingmacros\z@
-  \tracinglostchars\@ne
-  \tracingpages\z@
-  \tracingstats\z@
-}%
-\else
-\def\tracingnone{%
+\edef\tracingnone{%
   \tracingassigns\z@
   \tracingrestores\z@
   \tracingonline\z@
@@ -1563,6 +1627,7 @@
   \showboxbreadth\m@ne
   \tracingoutput\z@
   \errorcontextlines\m@ne
+  \ifdefined\tracingstacklevels \tracingstacklevels\z@ \fi
   \tracingnesting\z@
   \tracingscantokens\z@
   \tracingifs\z@
@@ -1573,30 +1638,77 @@
   \tracingpages\z@
   \tracingstats\z@
 }%
-\fi
+%</2ekernel|latexrelease>
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>
+%<latexrelease>\IncludeInRelease{2015/01/01}{\tracingnone}%
+%<latexrelease>                             {turn off etex tracing}%
+%<latexrelease>\ifx\tracingscantokens\@undefined
+%<latexrelease>\def\tracingnone{%
+%<latexrelease>  \tracingonline\z@
+%<latexrelease>  \tracingcommands\z@
+%<latexrelease>  \showboxdepth\m@ne
+%<latexrelease>  \showboxbreadth\m@ne
+%<latexrelease>  \tracingoutput\z@
+%<latexrelease>  \errorcontextlines\m@ne
+%<latexrelease>  \tracingrestores\z@
+%<latexrelease>  \tracingparagraphs\z@
+%<latexrelease>  \tracingmacros\z@
+%<latexrelease>  \tracinglostchars\@ne
+%<latexrelease>  \tracingpages\z@
+%<latexrelease>  \tracingstats\z@
+%<latexrelease>}%
+%<latexrelease>\else
+%<latexrelease>\def\tracingnone{%
+%<latexrelease>  \tracingassigns\z@
+%<latexrelease>  \tracingrestores\z@
+%<latexrelease>  \tracingonline\z@
+%<latexrelease>  \tracingcommands\z@
+%<latexrelease>  \showboxdepth\m@ne
+%<latexrelease>  \showboxbreadth\m@ne
+%<latexrelease>  \tracingoutput\z@
+%<latexrelease>  \errorcontextlines\m@ne
+%<latexrelease>  \tracingnesting\z@
+%<latexrelease>  \tracingscantokens\z@
+%<latexrelease>  \tracingifs\z@
+%<latexrelease>  \tracinggroups\z@
+%<latexrelease>  \tracingparagraphs\z@
+%<latexrelease>  \tracingmacros\z@
+%<latexrelease>  \tracinglostchars\@ne
+%<latexrelease>  \tracingpages\z@
+%<latexrelease>  \tracingstats\z@
+%<latexrelease>}%
+%<latexrelease>\fi
+%<latexrelease>\EndIncludeInRelease
+%<latexrelease>
+%<latexrelease>\IncludeInRelease{0000/00/00}{\tracingnone}%
+%<latexrelease>                             {turn off etex tracing}%
+%<latexrelease>\let\tracingnone\@undefined
+%<latexrelease>\EndIncludeInRelease
 %    \end{macrocode}
+% \end{macro}
 %
+% \begin{macro}{\hideoutput}
+% \changes{v2.0g}{2015/03/10}{macro added}
 %    \begin{macrocode}
+%<*2ekernel|latexrelease>
+%<latexrelease>\IncludeInRelease{2015/01/01}{\hideoutput}%
+%<latexrelease>                             {hide output from tracing}%
 \def\hideoutput{%
   \tracingoutput\z@
   \showboxbreadth\m@ne
   \showboxdepth\m@ne
   \tracingonline\m@ne
 }%
-%    \end{macrocode}
-%
-%    \begin{macrocode}
-%</2ekernel|latexrelease>
 %<latexrelease>\EndIncludeInRelease
-%<latexrelease>\IncludeInRelease{0000/00/00}{\tracingnone}%
-%<latexrelease>                             {turn off etex tracing}%
-%<latexrelease>\let\tracingnone\@undefined
+%<latexrelease>
+%<latexrelease>\IncludeInRelease{0000/00/00}{\hideoutput}%
+%<latexrelease>                             {hide output from tracing}%
 %<latexrelease>\let\hideoutput\@undefined
 %<latexrelease>\EndIncludeInRelease
+%</2ekernel|latexrelease>
 %    \end{macrocode}
 % \end{macro}
-% \end{macro}
-%
 %
 % \LaTeX\ change: |\showhyphens| Defined later.
 %
diff --git a/Master/texmf-dist/source/latex-dev/base/ltshipout.dtx b/Master/texmf-dist/source/latex-dev/base/ltshipout.dtx
index 565f35f529c..f773cd23da2 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltshipout.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltshipout.dtx
@@ -33,7 +33,7 @@
 %
 %    \begin{macrocode}
 \providecommand\ltshipoutversion{v1.0i}
-\providecommand\ltshipoutdate{2021/01/25}
+\providecommand\ltshipoutdate{2021/03/17}
 %    \end{macrocode}
 %
 %<*driver>
@@ -144,6 +144,12 @@
 %    This box register is called \cs{ShipoutBox} (alternatively
 %    available via the L3 name \cs{l_shipout_box}).
 %
+%    This box is a ``local'' box and assignments to it should be done
+%    only locally. Global assignments (as done by some packages with
+%    older code where this is box is known as 255) may work but they are
+%    conceptually wrong and may result in errors under certain
+%    circumstances.
+%
 %    During the execution of \hook{shipout/before} this box contains
 %    the accumulated material for the page, but not yet any material
 %    added by other shipout hooks.
diff --git a/Master/texmf-dist/source/latex-dev/base/lttab.dtx b/Master/texmf-dist/source/latex-dev/base/lttab.dtx
index a964b365753..48627f40a3c 100644
--- a/Master/texmf-dist/source/latex-dev/base/lttab.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/lttab.dtx
@@ -31,7 +31,7 @@
 %%% From File: lttab.dtx
 %<*driver>
 % \fi
-\ProvidesFile{lttab.dtx}[2020/04/24 v1.1r LaTeX Kernel (Columns)]
+\ProvidesFile{lttab.dtx}[2021/04/20 v1.1s LaTeX Kernel (Columns)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{lttab.dtx}
@@ -464,7 +464,7 @@
 %
 % \begin{macro}{\@tabcr}
 %    \begin{macrocode}
-\def\@tabcr{\@stopline \@ifstar{\penalty \@M \@xtabcr}\@xtabcr}
+\protected\def\@tabcr{\@stopline \@ifstar{\penalty \@M \@xtabcr}\@xtabcr}
 %    \end{macrocode}
 % \end{macro}
 %
@@ -964,8 +964,9 @@
 %
 %  \begin{macro}{\@arraycr}
 % Array version of |\\|.
+% \changes{v1.1s}{2021/04/20}{Use \cs{protected} for \cs{\bslash} variant (gh/548)}
 %    \begin{macrocode}
-\def\@arraycr{%
+\protected\def\@arraycr{%
   ${\ifnum0=`}\fi\@ifstar\@xarraycr\@xarraycr}
 %    \end{macrocode}
 % \end{macro}
@@ -994,8 +995,9 @@
 % \end{macro}
 %
 %  \begin{macro}{\@tabularcr}
+% \changes{v1.1s}{2021/04/20}{Use \cs{protected} for \cs{\bslash} variant (gh/548)}
 %    \begin{macrocode}
-\def\@tabularcr{%
+\protected\def\@tabularcr{%
   {\ifnum0=`}\fi\@ifstar\@xtabularcr\@xtabularcr}
 %    \end{macrocode}
 % \end{macro}
diff --git a/Master/texmf-dist/source/latex-dev/base/lttextcomp.dtx b/Master/texmf-dist/source/latex-dev/base/lttextcomp.dtx
index d840f0448b9..1efc36d5637 100644
--- a/Master/texmf-dist/source/latex-dev/base/lttextcomp.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/lttextcomp.dtx
@@ -36,7 +36,7 @@
 %
 %
 \ProvidesFile{lttextcomp.dtx}
-             [2021/01/20 v1.0d LaTeX Kernel (text companion symbols)]
+             [2021/04/16 v1.0f LaTeX Kernel (text companion symbols)]
 % \iffalse
 \documentclass{ltxdoc}
 \begin{document}
@@ -70,20 +70,23 @@
 %
 % \StopEventually{}
 %
+% \changes{v1.0e}{2021/03/19}
+%         {Use \cs{NewModuleRelease}}
+%    \begin{macrocode}
+%<*2ekernel|latexrelease>
+%<latexrelease>\NewModuleRelease{2020/02/02}{lttextcomp}
+%<latexrelease>                 {Text Companion symbols}
+%    \end{macrocode}
 %
 %  \begin{macro}{\oldstylenums}
 %  \begin{macro}{\legacyoldstylenums}
 %
-%
 %    Preserve the old definition of \cs{oldstylenums} under a different name.
 %
 %    This macro implements old style numerals but only works if we
 %    assume that the standard math fonts are used. Thus it needs
 %    changing in case other math encodings are used.
 %    \begin{macrocode}
-%<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2020/02/02}%
-%<latexrelease>                 {\oldstylenums}{Old style numerals}%
 \DeclareRobustCommand\legacyoldstylenums[1]{%
    \begingroup
 %    \end{macrocode}
@@ -157,44 +160,6 @@
 %    \end{macrocode}
 % \end{macro}
 %
-%
-%    \begin{macrocode}
-%</2ekernel|latexrelease>
-%<latexrelease>\EndIncludeInRelease
-%<latexrelease>\IncludeInRelease{0000/00/00}%
-%<latexrelease>                 {\oldstylenums}{Old style numerals}%
-%<latexrelease>
-%<latexrelease>\DeclareRobustCommand\oldstylenums[1]{%
-%<latexrelease>   \begingroup
-%<latexrelease>    \spaceskip\fontdimen\tw@\font
-%<latexrelease>    \usefont{OML}{\rmdefault}{\f@series}{it}%
-%<latexrelease>    \mathgroup\symletters #1%
-%<latexrelease>   \endgroup
-%<latexrelease>}
-%<latexrelease>\let\legacyoldstylenums\@undefined
-%<latexrelease>\def\textcompsubstdefault{cmr}
-%<latexrelease>
-%<latexrelease>\EndIncludeInRelease
-%    \end{macrocode}
-%
-%
-
-
-
-
-
-%    Everything else in the this file got introduced 2020/02/02, so we do a
-%    single rollback (for now).
-%    \begin{macrocode}
-%<*2ekernel>
-%</2ekernel>
-%<*2ekernel|latexrelease>
-%<latexrelease>\IncludeInRelease{2020/02/02}%
-%<latexrelease>   {\DeclareEncodingSubset}{Text companion symbols}%
-%    \end{macrocode}
-%
-%
-%
 %  \begin{macro}{\DeclareEncodingSubset}
 %
 %     The declaration takes 3 mandatory arguments: an \emph{encoding}
@@ -1300,9 +1265,19 @@
 % Supporting rollback \ldots
 %    \begin{macrocode}
 %</2ekernel|latexrelease>
-%<latexrelease>\EndIncludeInRelease
+%<latexrelease>
 %<latexrelease>\IncludeInRelease{0000/00/00}%
-%<latexrelease>   {\DeclareEncodingSubset}{Text companion symbols}%
+%<latexrelease>     {lttextcomp}{Undefine text companion symbols}%
+%<latexrelease>
+%<latexrelease>\DeclareRobustCommand\oldstylenums[1]{%
+%<latexrelease>   \begingroup
+%<latexrelease>    \spaceskip\fontdimen\tw@\font
+%<latexrelease>    \usefont{OML}{\rmdefault}{\f@series}{it}%
+%<latexrelease>    \mathgroup\symletters #1%
+%<latexrelease>   \endgroup
+%<latexrelease>}
+%<latexrelease>\let\legacyoldstylenums\@undefined
+%<latexrelease>\def\textcompsubstdefault{cmr}
 %<latexrelease>
 %<latexrelease>\let\DeclareEncodingSubset\@undefined
 %<latexrelease>\let\CheckEncodingSubset\@undefined
@@ -1493,9 +1468,7 @@
 %<latexrelease>\let\textlegacyperiodcentered\@undefined
 %<latexrelease>\let\textlegacysection\@undefined
 %<latexrelease>
-%<latexrelease>\EndIncludeInRelease
-%<*2ekernel>
-%</2ekernel>
+%<latexrelease>\EndModuleRelease
 %    \end{macrocode}
 %
 %
diff --git a/Master/texmf-dist/source/latex-dev/base/ltvers.dtx b/Master/texmf-dist/source/latex-dev/base/ltvers.dtx
index 26eaee98901..fe50d75a8f1 100644
--- a/Master/texmf-dist/source/latex-dev/base/ltvers.dtx
+++ b/Master/texmf-dist/source/latex-dev/base/ltvers.dtx
@@ -33,7 +33,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{ltvers.dtx}
-             [2021/01/15 v1.1e LaTeX Kernel (Version Info)]
+             [2021/04/16 v1.1g LaTeX Kernel (Version Info)]
 % \iffalse
 \documentclass{ltxdoc}
 \GetFileInfo{ltvers.dtx}
@@ -112,10 +112,10 @@
 %</2ekernel>
 %<latexrelease>\edef\latexreleaseversion
 %<*2ekernel|latexrelease>
-   {2021-05-01}
+   {2021-06-01}
 %</2ekernel|latexrelease>
 %<*2ekernel>
-\def\patch@level{-2}
+\def\patch@level{-3}
 %    \end{macrocode}
 %
 % \begin{macro}{\development@branch@name}
@@ -214,6 +214,11 @@
 %    \end{macrocode}
 %
 % \begin{macro}{\IncludeInRelease}
+% \begin{macro}{\EndIncludeInRelease}
+% \begin{macro}{\@IncludeInRelease}
+% \begin{macro}{\@IncludeInRele@se}
+% \begin{macro}{\@gobble@IncludeInRelease}
+% \begin{macro}{\@check@IncludeInRelease}
 % \changes{v1.0w}{2015/02/21}
 %         {set \cs{@currname} empty here (in case \cs{IncludeInRelease} input early)}
 %    \begin{macrocode}
@@ -224,6 +229,7 @@
 % \changes{v1.0m}{2015/01/17}{modified with \cs{@currname}}
 % \changes{v1.0o}{2015/01/19}{Optional argument}
 % \changes{v1.0q}{2015/02/19}{Swap argument order}
+% \changes{v1.1f}{2021/03/18}{Add support for usage in \cs{NewModuleRelease}}
 %
 %    \begin{macrocode}
 %<*2ekernel|latexrelease>
@@ -237,9 +243,29 @@
                 {There is an \string\EndIncludeRelease\space missing}%
   \@includeinreleasefalse
   \fi
-  \kernel@ifnextchar[%
-  {\@IncludeInRelease{#1}}
-  {\@IncludeInRelease{#1}[#1]}}
+  \ifnum0%
+      \ifx\new@moduledate\@empty\else 1\fi
+      \ifnum \expandafter\@parse@version#1//00\@nil=0 1\fi
+      =11
+    \expandafter\@firstoftwo
+  \else
+    \expandafter\@secondoftwo
+  \fi
+    {\finish@module@release{#1}}%
+    {\kernel@ifnextchar[%
+      {\@IncludeInRelease{#1}}
+      {\@IncludeInRelease{#1}[#1]}}}
+\def\finish@module@release#1#2#3{%
+  \toks@{[#1] #3}%
+  \ifnum\expandafter\@parse@version\new@moduledate//00\@nil
+       >\expandafter\@parse@version\fmtversion//00\@nil
+    \GenericInfo{}{Applying: \the\toks@}%
+  \else
+    \GenericInfo{}{Skipping: \the\toks@}%
+    \expandafter\gobble@finish@module@release
+  \fi}
+\long\def\gobble@finish@module@release#1\EndModuleRelease{%
+  \EndModuleRelease}
 %    \end{macrocode}
 %
 % If a specific date has not been specified in |latexrelease|
@@ -261,9 +287,9 @@
 %    only really needed for rolling forward. So maybe one day \dots
 %    \begin{macrocode}
     \ifnum\expandafter\@parse@version#1//00\@nil
-          >\expandafter\@parse@version\fmtversion//00\@nil
+         >\expandafter\@parse@version\fmtversion//00\@nil
       \GenericInfo{}{Skipping: \the\toks@}%
-     \expandafter\expandafter\expandafter\@gobble@IncludeInRelease
+      \expandafter\expandafter\expandafter\@gobble@IncludeInRelease
     \else
       \GenericInfo{}{Applying: \the\toks@}%
       \@includeinreleasetrue
@@ -282,6 +308,9 @@
   \@includeinreleasefalse
 \else
   \PackageError{latexrelease}{mis-matched EndIncludeInRelease}{}%
+\fi
+\if@skipping@module
+  \expandafter\new@module@skip
 \fi}
 %    \end{macrocode}
 %
@@ -296,13 +325,87 @@
                                    #2#3\@end@check@IncludeInRelease{%
   \ifx\@check@IncludeInRelease#2\else
     \PackageError{latexrelease}{skipped IncludeInRelease for tag \string#2}{}%
+  \fi
+  \if@skipping@module
+    \expandafter\new@module@skip
   \fi}
 %    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
 %
+% \subsection{Declaring an all-new module}
+%
+% \begin{macro}{\if@skipping@module}
+% \begin{macro}{\NewModuleRelease}
+% \begin{macro}{\EndModuleRelease}
+% \begin{macro}{\new@module@skip}
+% \begin{macro}{\new@modulename}
+% \begin{macro}{\new@moduledate}
+%
+%   When we have a whole new module, we can't roll back to a date where
+%   such module exists, otherwise hundreds of \enquote{command already
+%   defined} errors will pop up.  But we can't skip it altogether
+%   either, because the module might have changes we still want applied,
+%   so a more detailed cherry-picking of code chunks have to be done.
+%
+%   \changes{v1.1f}{2021/03/18}{Added \cs{NewModuleRelease}.}
+%   \changes{v1.1g}{2021/04/16}
+%           {\cs{NewModuleRelease} with the same arguments as \cs{IncludeInRelease}.}
 %    \begin{macrocode}
-%</2ekernel|latexrelease>
+\let\if@skipping@module\iffalse
+\def\@skipping@moduletrue{\let\if@skipping@module\iftrue}
+\def\@skipping@modulefalse{\let\if@skipping@module\iffalse}
+\let\new@modulename\@empty
+\let\new@moduledate\@empty
+\def\NewModuleRelease#1#2#3{%
+  \ifx\new@modulename\@empty \else
+    \@latex@error{Nested \noexpand\NewModuleRelease forbidden.}\@ehd \fi
+  \edef\new@moduledate{#1}%
+  \edef\new@modulename{#2}%
+  \GenericInfo{}{BEGIN module: \new@modulename\space (\new@moduledate)}%
+  \GenericInfo{}{ \@spaces\@spaces\@spaces\space#3\@gobble}%
+  \ifnum\sourceLaTeXdate<%
+      \expandafter\@parse@version\new@moduledate//00\@nil\relax
+    \ifnum\expandafter\@parse@version\fmtversion//00\@nil<%
+          \expandafter\@parse@version\new@moduledate//00\@nil\relax
+      \GenericInfo{}{Skipping module \new@modulename}%
+      \expandafter\expandafter
+      \expandafter\gobble@finish@module@release
+    \else
+      \GenericInfo{}{Applying module \new@modulename}
+      \@skipping@modulefalse
+    \fi
+  \else
+    \GenericInfo{}{Skipping module \new@modulename}
+    \@skipping@moduletrue
+    \expandafter\new@module@skip
+  \fi}
+\long\def\new@module@skip#1\IncludeInRelease{\IncludeInRelease}
+\def\EndModuleRelease{%
+  \ifx\new@modulename\@empty
+    \@latex@error{Extra \string\EndModuleRelease.}\@eha
+  \else
+    \GenericInfo{}{END module: \new@modulename\space (\new@moduledate)}%
+    \let\new@modulename\@empty
+    \let\new@moduledate\@empty
+    \@skipping@modulefalse
+  \fi}
 %    \end{macrocode}
 % \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+% \end{macro}
+%
+%    \begin{macrocode}
+%</2ekernel|latexrelease>
+%    \end{macrocode}
+%
 % \Finale
 %
 \endinput
diff --git a/Master/texmf-dist/source/latex-dev/graphics/color.dtx b/Master/texmf-dist/source/latex-dev/graphics/color.dtx
index cdc2dbe5fed..2dfbb238daa 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/color.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/color.dtx
@@ -2,7 +2,9 @@
 % \iffalse
 %
 %% color.dtx Copyright (C) 1994--1999 David Carlisle
-%%           Copyright (C) 2005-2020 David Carlisle, LaTeX3 Project
+%%           Copyright (C) 2005-2021
+%% The LaTeX Project and any individual authors listed elsewhere
+%% in this file.
 %%
 %% This file is part of the Standard LaTeX `Graphics Bundle'.
 %% It may be distributed under the terms of the LaTeX Project Public
diff --git a/Master/texmf-dist/source/latex-dev/graphics/drivers.dtx b/Master/texmf-dist/source/latex-dev/graphics/drivers.dtx
index 9bf32f78a1f..6704ad11c68 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/drivers.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/drivers.dtx
@@ -3,7 +3,9 @@
 %
 %% drivers.dtx Copyright (C) 1994      David Carlisle Sebastian Rahtz
 %%             Copyright (C) 1995 1996 1997 1998 1999 David Carlisle
-%%             Copyright (C) 2000-2020 David Carlisle, LaTeX3 Project
+%%             Copyright (C) 2000-2021
+%% The LaTeX Project and any individual authors listed elsewhere
+%% in this file.
 %%
 %% This file is part of the Standard LaTeX `Graphics Bundle'.
 %% It may be distributed under the terms of the LaTeX Project Public
diff --git a/Master/texmf-dist/source/latex-dev/graphics/epsfig.dtx b/Master/texmf-dist/source/latex-dev/graphics/epsfig.dtx
index 8e883bd8df7..a34aa6842ee 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/epsfig.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/epsfig.dtx
@@ -2,7 +2,9 @@
 % \iffalse
 %
 %% epsfig.dtx Copyright (C) 1994-1996 1999 Sebastian Rahtz
-%%            Copyright (C) 2000-2020 David Carlisle, LaTeX3 Project
+%%            Copyright (C) 2000-2021
+%% The LaTeX Project and any individual authors listed elsewhere
+%% in this file.
 %%
 %% This file is part of the Standard LaTeX `Graphics Bundle'.
 %% It may be distributed under the terms of the LaTeX Project Public
diff --git a/Master/texmf-dist/source/latex-dev/graphics/graphics.dtx b/Master/texmf-dist/source/latex-dev/graphics/graphics.dtx
index 51ef9a4ee39..0c5c9e88eca 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/graphics.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/graphics.dtx
@@ -2,7 +2,9 @@
 % \iffalse
 %
 %% graphics.dtx Copyright (C) 1994      David Carlisle Sebastian Rahtz
-%%              Copyright (C) 1995-2020 David Carlisle, LaTeX3 Project
+%%              Copyright (C) 1995-2021
+%% The LaTeX Project and any individual authors listed elsewhere
+%% in this file.
 %%
 %% This file is part of the Standard LaTeX `Graphics Bundle'.
 %% It may be distributed under the terms of the LaTeX Project Public
@@ -25,7 +27,7 @@
 %<driver> \ProvidesFile{graphics.drv}
 % \fi
 %         \ProvidesFile{graphics.dtx}
-          [2020/08/30 v1.4c  Standard LaTeX Graphics (DPC,SPQR)]
+          [2021/03/04 v1.4d  Standard LaTeX Graphics (DPC,SPQR)]
 %
 % \iffalse
 %<*driver>
@@ -1123,7 +1125,12 @@
     \ifx\filename@ext\relax
       \let\filename@ext\Gin@gzext
     \else
-      \edef\Gin@ext{\Gin@ext\Gin@sepdefault\Gin@gzext}%
+%    \end{macrocode}
+% \changes{v1.4d}{2021/03/04}
+%     {\cs{filename@ext} instead of \cs{Gin@ext} when
+%      checking for \texttt{gzip}ped graphics file.}
+%    \begin{macrocode}
+      \edef\filename@ext{\filename@ext\Gin@sepdefault\Gin@gzext}%
     \fi
   \fi
   \ifx\filename@ext\relax
@@ -1146,14 +1153,17 @@
 %     {Try adding an extension even if the filename had a dot AND
 %      if the filename without the extension exists (but doesn't have
 %      a known extension).}
+% \changes{v1.4d}{2021/03/03}
+%     {Avoid warning when loading a file using a generic rule.}
 %    \begin{macrocode}
     \ifnum0%
         \ifx\Gin@ext\relax 1%
         \else \@ifundefined{Gin@rule@\Gin@ext}{1}{0}%
         \fi >0
-      \let\Gin@ext\relax
+      \let\Gin@extsaved\Gin@ext
       \let\Gin@savedbase\filename@base
       \let\Gin@savedext\filename@ext
+      \let\Gin@ext\relax
       \edef\filename@base{\filename@base\Gin@sepdefault\filename@ext}%
       \let\filename@ext\relax
       \@for\Gin@temp:=\Gin@extensions\do{%
@@ -1164,6 +1174,7 @@
 % Restore if no file found using the known extensions.
 %    \begin{macrocode}
       \ifx\Gin@ext\relax
+        \let\Gin@ext\Gin@extsaved
         \let\filename@base\Gin@savedbase
         \let\filename@ext\Gin@savedext
       \fi
diff --git a/Master/texmf-dist/source/latex-dev/graphics/graphicx.dtx b/Master/texmf-dist/source/latex-dev/graphics/graphicx.dtx
index b10c67c7946..a2fc17e3936 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/graphicx.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/graphicx.dtx
@@ -2,7 +2,9 @@
 % \iffalse
 %
 %% graphicx.dtx Copyright (C) 1994      David Carlisle Sebastian Rahtz
-%%              Copyright (C) 1995-2020 David Carlisle, LaTeX3 Project
+%%              Copyright (C) 1995-2021
+%% The LaTeX Project and any individual authors listed elsewhere
+%% in this file.
 %%
 %% This file is part of the Standard LaTeX `Graphics Bundle'.
 %% It may be distributed under the terms of the LaTeX Project Public
@@ -17,7 +19,7 @@
 %<driver> \ProvidesFile{graphicx.drv}
 % \fi
 %         \ProvidesFile{graphicx.dtx}
-          [2020/09/09 v1.2b  Enhanced LaTeX Graphics (DPC,SPQR)]
+          [2020/12/05 v1.2c  Enhanced LaTeX Graphics (DPC,SPQR)]
 %
 % \iffalse
 %<*driver>
@@ -88,7 +90,7 @@
 % name (or key) and any options that must be set are set by explicitly
 % associating this name with the desired value.
 %
-% The members of the \LaTeX3 project do appreciate the importance of
+% The members of the \LaTeX\ Project do appreciate the importance of
 % this kind of syntax, but felt that rather than extending the syntax of
 % \LaTeX\ in an uncoordinated way, it would be better to keep with
 % `standard arguments' in \LaTeXe, which is intended as a `consolidation
@@ -507,9 +509,10 @@
 %
 % \begin{key}{Gin}{quiet}
 % \changes{v1.1a}{2017/06/01}{New quiet key}
+% \changes{v1.2c}{2020/12/05}{fix missing default value}
 %   Skip writing to the log.
 %    \begin{macrocode}
-\define@key{Gin}{quiet}{%
+\define@key{Gin}{quiet}[]{%
   \let\Gin@log\@gobble
 }
 %    \end{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/graphics/keyval.dtx b/Master/texmf-dist/source/latex-dev/graphics/keyval.dtx
index dd1f542832c..58664b8f037 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/keyval.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/keyval.dtx
@@ -1,7 +1,9 @@
 %
 % \iffalse
 %% keyval.dtx Copyright (C) 1993 1994 1995 1997 1998 1999 David Carlisle
-%%            Copyright (C) 2000-2020 David Carlisle, LaTeX3 Project
+%%            Copyright (C) 2000-2021 David Carlisle, LaTeX Project
+%% The LaTeX Project and any individual authors listed elsewhere
+%% in this file.
 %%
 %% This file is part of the Standard LaTeX `Graphics Bundle'.
 %% It may be distributed under the terms of the LaTeX Project Public
diff --git a/Master/texmf-dist/source/latex-dev/graphics/lscape.dtx b/Master/texmf-dist/source/latex-dev/graphics/lscape.dtx
index ac5c16d7c20..969c94ae7a8 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/lscape.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/lscape.dtx
@@ -2,7 +2,9 @@
 % \iffalse
 %
 %% lscape.dtx Copyright (C) 1994 1999-2000 David Carlisle
-%%            Copyright (C) 2000-2020 David Carlisle, LaTeX3 Project
+%%            Copyright (C) 2000-2021
+%% The LaTeX Project and any individual authors listed elsewhere
+%% in this file.
 %%
 %% This file is part of the Standard LaTeX `Graphics Bundle'.
 %% It may be distributed under the terms of the LaTeX Project Public
diff --git a/Master/texmf-dist/source/latex-dev/graphics/rotating.dtx b/Master/texmf-dist/source/latex-dev/graphics/rotating.dtx
index 535f115594b..c6db1273a43 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/rotating.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/rotating.dtx
@@ -3,9 +3,11 @@
 %
 %
 % File: rotating.dtx
-%% Copyright (C) 1995--1999 Sebastian Rahtz and Leonor Barroca
-%% Copyright (C) 2001--2003,2007--2009 Robin Fairbairns
-%% Copyright (C) 2016-2020 LaTeX3 Project
+%% Copyright (C) 1995-1999 Sebastian Rahtz and Leonor Barroca
+%% Copyright (C) 2001-2003,2007-2009 Robin Fairbairns
+%% Copyright (C) 2016-2021 LaTeX Project
+%% The LaTeX Project and any individual authors listed elsewhere
+%% in this file.
 %
 % This work may be distributed and/or modified under the
 % conditions of the LaTeX Project Public License, either version 1.3c
diff --git a/Master/texmf-dist/source/latex-dev/graphics/trig.dtx b/Master/texmf-dist/source/latex-dev/graphics/trig.dtx
index 67f6c6a9703..83e774ff20b 100644
--- a/Master/texmf-dist/source/latex-dev/graphics/trig.dtx
+++ b/Master/texmf-dist/source/latex-dev/graphics/trig.dtx
@@ -1,6 +1,8 @@
 % \iffalse
-%% File: trig.dtx Copyright (C) 1993 1994 1995 1996 1997 1999 David Carlisle
-%%                Copyright (C) 2000-2020 David Carlisle, LaTeX3 Project
+%% File: trig.dtx Copyright (C) 1993-1999 David Carlisle
+%%                Copyright (C) 2000-2021
+%% The LaTeX Project and any individual authors listed elsewhere
+%% in this file.
 %%
 %% This file is part of the Standard LaTeX `Graphics Bundle'.
 %% It may be distributed under the terms of the LaTeX Project Public
diff --git a/Master/texmf-dist/source/latex-dev/tools/array.dtx b/Master/texmf-dist/source/latex-dev/tools/array.dtx
index 1ca08036d95..84376a486b3 100644
--- a/Master/texmf-dist/source/latex-dev/tools/array.dtx
+++ b/Master/texmf-dist/source/latex-dev/tools/array.dtx
@@ -33,7 +33,7 @@
 %<+package>\DeclareCurrentRelease{}{2020-10-01}
 %<+package>
 %<+package>\ProvidesPackage{array}
-%<+package>         [2021/02/10 v2.5d Tabular extension package (FMi)]
+%<+package>         [2021/04/20 v2.5e Tabular extension package (FMi)]
 %
 % \fi
 %
@@ -2193,8 +2193,9 @@
 %    For further information see
 %    \cite[Appendix D]{bk:knuth}.
 % \changes{v2.3c}{1995/04/23}{Avoid adding an ord atom in math}
+% \changes{v2.5e}{2021/04/20}{Use \cs{protected} for \cs{\bslash} variant (gh/548)}
 %    \begin{macrocode}
-\def\@arraycr{\relax\iffalse{\fi\ifnum 0=`}\fi
+\protected\def\@arraycr{\relax\iffalse{\fi\ifnum 0=`}\fi
 %    \end{macrocode}
 %    Then we test whether the user is using the star form and ignore
 %    a possible star (I also disagree with this procedure, because a
diff --git a/Master/texmf-dist/source/latex-dev/tools/bm.dtx b/Master/texmf-dist/source/latex-dev/tools/bm.dtx
index 80c73f57189..2b56b92b547 100644
--- a/Master/texmf-dist/source/latex-dev/tools/bm.dtx
+++ b/Master/texmf-dist/source/latex-dev/tools/bm.dtx
@@ -36,7 +36,7 @@
 %<driver>\ProvidesFile{bm.drv}
 % \fi
 %         \ProvidesFile{bm.dtx}
-          [2019/07/24 v1.2d Bold Symbol Support (DPC/FMi)]
+          [2021/04/25 v1.2e Bold Symbol Support (DPC/FMi)]
 %
 % \iffalse
 %<*driver>
@@ -295,6 +295,23 @@
 % between these two packages, this package defines |\boldsymbol| and
 % |\heavysymbol| as alternative names for |\bm| and |\hm|.
 %
+% \section{Package Options}
+%
+% \subsection{Logging level}
+% As described above, the \textsf{bm} package has to interrogate the font
+% setup to try to find matching bold fonts for each font used in the |normal|
+% math version. This can fail in various ways as there may be no bold font
+% or a bold font may be found but no room is available to allocate it.
+% The options |warn|, |info| and |silent| control whether messages that \textsf{bm}
+% produces are sent to the terminal, or just to the log file (the default) or suppressed.
+%
+% \subsection{Poor Man's Bold}
+% As discussed above, by default, if no real bold font is available, \textsf{bm} will use
+% ``poor man's bold''. That is, over-printing the character with slight offsets.
+% Since version 1.2e, the package now warns if a font is set up to use this over-printing and
+% the package option |nopbm|  is available which prevents its use in which case |\bm| will
+% use the non-bold for characters from the affected font,
+%
 % \StopEventually{}
 %
 % \section{Implementation}
@@ -320,6 +337,20 @@
 %      {minor doc changes latex/3058}
 %
 %
+% \changes{v1.2e}{2021/04/25}
+%      {Package options gh/71}
+% Options to use or not use poor mans bold (over-printing)
+% and level of warning messages.
+%    \begin{macrocode}
+%<*package>
+\DeclareOption{nopmb}{\let\bm@pmb@\@firstofone}
+\DeclareOption{warn}{\def\bm@info{\PackageWarningNoLine{bm}}}
+\DeclareOption{info}{\def\bm@info#1{\PackageInfo{bm}{#1\@gobble}}}
+\DeclareOption{silent}{\let\bm@info\@gobble}
+\ExecuteOptions{info}
+\ProcessOptions\relax
+%</package>
+%    \end{macrocode}
 %
 % The commands |\bm| and |\hm| work by defining a number of additional
 % symbol fonts corresponding to the standard ones
@@ -368,6 +399,7 @@
 % code, which is temporarily defined to |\bm|, to save wasting a csname.
 % Similarly |\bm@pmb|\ldots\ (which will be defined later) are used
 % as scratch macros.
+% (This csname saving no longer used, setup command is |\bm@setup| not |\bm|).
 %
 % The general plan. Run through the fonts allocated to the normal math
 % version. Ignore \meta{math alphabet} allocations\footnote{For now?}
@@ -393,15 +425,15 @@
 % using |\boldmath| or poor man's bold.)
 %
 %    \begin{macrocode}
-\def\bm#1#2{%
+\def\bm@setup#1#2{%
 %    \end{macrocode}
 % This code can not work inside a group, as that would affect any symbol
 % font allocations, so instead use some scratch macros to save and
 % restore the definitions of commands we need to change locally.
 %    \begin{macrocode}
-  \let\bm@pmb\install@mathalphabet
-  \let\bm@pmb@\getanddefine@fonts
-  \let\bm@pmb@@\or
+  \let\bm@install@mathalphabet\install@mathalphabet
+  \let\bm@getanddefine@fonts\getanddefine@fonts
+  \let\bm@or\or
   \edef\bm@general{\f@encoding/\f@family/\f@series/\f@shape/\f@size}%
 %    \end{macrocode}
 %
@@ -465,8 +497,12 @@
 %    \end{macrocode}
 % If they are the same, set this offset to $-1$, as a flag to use
 % poor man's bold.
+% \changes{v1.2e}{2021/04/25}
+%      {make use of pmb optional and warn about it gh/71}
 %    \begin{macrocode}
       \bm@define\m@ne
+      \bm@info{No #1 for \string##2%
+               \ifx\bm@pmb@\@firstofone\else, using \string\pmb\fi}%
     \else
 %    \end{macrocode}
 % Else make a new name by adjoining |#1| to the name of the symbol font
@@ -569,7 +605,7 @@
 %    \end{macrocode}
 % If the font has been allocated already, use the existing allocation.
 %    \begin{macrocode}
-          \PackageInfo{bm}%
+          \bm@info
             {Symbol font \@tempa\space already defined.\MessageBreak
              Not overwriting it}%
         \fi
@@ -613,9 +649,9 @@
 % Put things back as they were.
 %    \begin{macrocode}
   \expandafter\split@name\bm@general\@nil
-  \let\install@mathalphabet\bm@pmb
-  \let\getanddefine@fonts\bm@pmb@
-  \let\or\bm@pmb@@}
+  \let\install@mathalphabet\bm@install@mathalphabet
+  \let\getanddefine@fonts\bm@getanddefine@fonts
+  \let\or\bm@or}
 %    \end{macrocode}
 % \end{macro}
 % \end{macro}
@@ -647,13 +683,13 @@
   \def\bm@boldtable{\m@ne}
   \AtEndOfPackage{%
     \def\bm@gr@up#1#2{%
-      \bm@pmb{#2}}}
+      \bm@install@mathalphabet{#2}}}
 \else
 %    \end{macrocode}
 % Otherwise use the definition of |\bm| above to set up |\bm@boldtable|
 % by comparing the fonts available in the normal and bold math versions.
 %    \begin{macrocode}
-  \bm{bold}\bmmax
+  \bm@setup{bold}\bmmax
 %    \end{macrocode}
 %
 % \begin{macro}{\mathbf}
@@ -689,7 +725,7 @@
 %    \begin{macrocode}
 \ifx\mv@heavy\@undefined
 \else
-  \bm{heavy}\hmmax
+  \bm@setup{heavy}\hmmax
 \fi
 %    \end{macrocode}
 % \end{macro}
@@ -781,6 +817,8 @@
 % you put something really strange in the arguments.
 % \changes{v0.11}{1997/01/06}
 %      {\cs{@ifnextchar} made safe.}
+% \changes{v1.2e}{2021/04/25}
+%      {treat \cs{kernel@ifnextchar} like \cs{@ifnextchar}}
 %    \begin{macrocode}
     \def\@ifnextchar##1##2##3##4{%
       \if##1##4%
@@ -789,6 +827,7 @@
         \expandafter\@secondoftwo
       \fi
       {##2##4}{##3{##4}}}%
+    \let\kernel@ifnextchar\@ifnextchar
 %    \end{macrocode}
 % For Vladimir Volovich\ldots
 % \changes{v1.0f}{1998/12/10}
@@ -1397,6 +1436,8 @@
 % \begin{macro}{\bm@pmb}
 % \changes{v0.10}{1997/01/04}
 %      {Macro added}
+% \changes{v1.2e}{2021/04/25}
+%      {option to make pmb a no-op}
 % Add a poor man's bold construction to the list being built.
 %    \begin{macrocode}
 \def\bm@pmb#1{%
@@ -1410,6 +1451,7 @@
 % |\pmb| variant. (See \TeX{}Book, or AMS \textsf{amsbsy} package).
 % This one takes a bit more care to use smaller offsets in subscripts.
 %    \begin{macrocode}
+\ifx\bm@pmb@\@firstofone\else
 \def\bm@pmb@#1{{%
   \setbox\tw@\hbox{$\m@th\mkern.4mu$}%
   \mathchoice
@@ -1434,6 +1476,7 @@
   \raise1.5\dimen@\rlap{\copy\z@}%
   \kern\dimen@
   \box\z@}}%
+\fi
 %    \end{macrocode}
 % \end{macro}
 %
diff --git a/Master/texmf-dist/source/latex-dev/tools/layout.dtx b/Master/texmf-dist/source/latex-dev/tools/layout.dtx
index 6962674255b..de61aeae8c4 100644
--- a/Master/texmf-dist/source/latex-dev/tools/layout.dtx
+++ b/Master/texmf-dist/source/latex-dev/tools/layout.dtx
@@ -30,7 +30,7 @@
 %<+package>\ProvidesPackage{layout}
 %<+driver>\ProvidesFile{layout.drv}
 %\ProvidesFile{layout.dtx}
-                [2020-07-25 v1.2d Show layout parameters]
+                [2021-03-10 v1.2e Show layout parameters]
 %
 %    A short driver is provided that can be extracted if necessary by
 %    the \textsf{DocStrip} program provided with \LaTeXe.
@@ -184,6 +184,18 @@
   }
 %    \end{macrocode}
 %    
+% \changes{v1.2e}{2021-03-10}{Added option for Romanian (gh529)}
+%    \begin{macrocode}
+\DeclareOption{romanian}{%
+  \def\Headertext{Antet}
+  \def\Bodytext{Corp}
+  \def\Footertext{Subsol}
+  \def\MarginNotestext{Note\\ Marginale}
+  \def\oneinchtext{un inch}
+  \def\notshown{neafi\textcommabelow sat}
+  }
+%    \end{macrocode}
+%    
 %    \changes{v1.2d}{2020-07-25}{Added option for Japanese (gh353)}
 % \begin{allowtofu}
 %    \begin{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/tools/longtable.dtx b/Master/texmf-dist/source/latex-dev/tools/longtable.dtx
index c236aabb205..5569ae3d5c8 100644
--- a/Master/texmf-dist/source/latex-dev/tools/longtable.dtx
+++ b/Master/texmf-dist/source/latex-dev/tools/longtable.dtx
@@ -30,14 +30,14 @@
 %<package>\providecommand\DeclareRelease[3]{}
 %<package>\providecommand\DeclareCurrentRelease[2]{}
 %<package>
-%<package>\DeclareRelease{}{2020-01-02}{longtable-2020-01-07.sty}
+%<package>\DeclareRelease{v4.13}{2020-01-02}{longtable-2020-01-07.sty}
 %<package>\DeclareCurrentRelease{}{2020-02-07}
 %<package>
 %<package>\ProvidesPackage{longtable}
 %<driver> \ProvidesFile{longtable.drv}
 % \fi
 %         \ProvidesFile{longtable.dtx}
-          [2020-02-07 v4.14 Multi-page Table package (DPC)]
+          [2021-04-21 v4.15 Multi-page Table package (DPC)]
 %
 % \iffalse
 %<*driver>
@@ -1282,6 +1282,8 @@
 %    \end{macrocode}
 % \changes{v3.16}{1995/11/09}
 %      {Measure the first line of the table}
+% \changes{v4.15}{2021/04/18}
+%      {silence \cs{vbadness}}
 % At this point I used to add "\ht\@arstrutbox" and "\dp\@arstrutbox"
 % as a measure of a row size. However this can fail spectacularly
 % for "p" columns which might be much larger. Previous versions could
@@ -1289,12 +1291,13 @@
 % a head \emph{then} a `first head'! So now measure the first line of
 % the table accurately by "\vsplit"ting it out of the first chunk.
 %    \begin{macrocode}
-  \dimen@ii\vfuzz
+  \edef\LT@reset@vfuzz{\vfuzz\the\vfuzz\vbadness\the\vbadness\relax}%
   \vfuzz\maxdimen
-    \setbox\tw@\copy\z@
-    \setbox\tw@\vsplit\tw@ to \ht\@arstrutbox
-    \setbox\tw@\vbox{\unvbox\tw@}%
-  \vfuzz\dimen@ii
+  \vbadness\@M
+  \setbox\tw@\copy\z@
+  \setbox\tw@\vsplit\tw@ to \ht\@arstrutbox
+  \setbox\tw@\vbox{\unvbox\tw@}%
+  \LT@reset@vfuzz
   \advance\dimen@ \ht
         \ifdim\ht\@arstrutbox>\ht\tw@\@arstrutbox\else\tw@\fi
   \advance\dimen@\dp
@@ -1498,8 +1501,10 @@
 % So use the following variant. Added in v3.14.
 % \changes{v3.14}{1995/04/25}
 %      {More fun with \cs{ifnum} cf tools/1571}
+% \changes{v4.15}{2021/04/21}
+%      {protected (gh/584)}
 %    \begin{macrocode}
-\def\LT@tabularcr{%
+\protected\def\LT@tabularcr{%
   \relax\iffalse{\fi\ifnum0=`}\fi
   \@ifstar
     {\def\crcr{\LT@crcr\noalign{\nobreak}}\let\cr\crcr
@@ -2000,6 +2005,8 @@
 %       and modified to call \cs{@makecaption}}
 % \changes{v3.14}{1995/05/02}
 %      {Use the first arg to remove counter for star form}
+% \changes{v4.15}{2021/03/28}
+%      {\cs{reset@font} for gh/133}
 %    \begin{macrocode}
 \def\LT@makecaption#1#2#3{%
   \LT@mcol\LT@cols c{\hbox to\z@{\hss\parbox[t]\LTcapwidth{%
@@ -2007,6 +2014,7 @@
 % Based on article class "\@makecaption", "#1" is "\@gobble" in star
 % form, and "\@firstofone" otherwise.
 %    \begin{macrocode}
+    \reset@font
     \sbox\@tempboxa{#1{#2: }#3}%
     \ifdim\wd\@tempboxa>\hsize
       #1{#2: }#3%
@@ -2219,10 +2227,12 @@
 % \end{macro}
 %
 % \begin{macro}{\LT@p@ftntext}
+% \changes{v4.15}{2021/03/28}
+%      {make long for gh/364}
 % Inside the `p' column, just save up the footnote text in a token
 % register.
 %    \begin{macrocode}
-\def\LT@p@ftntext#1{%
+\long\def\LT@p@ftntext#1{%
   \edef\@tempa{\the\LT@p@ftn\noexpand\footnotetext[\the\c@footnote]}%
   \global\LT@p@ftn\expandafter{\@tempa{#1}}}%
 %    \end{macrocode}
diff --git a/Master/texmf-dist/source/latex-dev/tools/trace.dtx b/Master/texmf-dist/source/latex-dev/tools/trace.dtx
index 7ab6e18e25b..d10243f690b 100644
--- a/Master/texmf-dist/source/latex-dev/tools/trace.dtx
+++ b/Master/texmf-dist/source/latex-dev/tools/trace.dtx
@@ -33,7 +33,7 @@
 %<driver>\ProvidesFile{trace.drv}
 % \fi
 %         \ProvidesFile{trace.dtx}
-          [2018/10/13 v1.1e trace LaTeX code]
+          [2021/04/18 v1.1f trace LaTeX code]
 %
 % \iffalse
 %<*driver>
@@ -343,7 +343,7 @@
 %
 % \begin{macro}{\traceon}
 %    This macro ensures that |\conditionally@traceoff| is actually
-%    turning off switches (since |\tracinall| might have disabled it)
+%    turning off switches (since |\tracingall| might have disabled it)
 %    and then calls |\tr@ce@n| to setup tracing.
 %    \begin{macrocode}
 \def\traceon{\let\conditionally@traceoff\unconditionally@traceoff
@@ -470,6 +470,8 @@
 %    |\tr@ce@n|, however there is no point in resetting
 %    |\tracinglostchars| so we leave it alone.
 %  \changes{v1.1c}{2003/04/30}{Reset \cs{tracingstats} to one}
+%  \changes{v1.1f}{2021/04/18}
+%                {Add \cs{tracingstacklevels} and \cs{tracinglostchars}=3}
 %    \begin{macrocode}
 %   \tracingstats\@ne
 %% \tracinglostchars\z@
@@ -498,13 +500,14 @@
 %    on last (in fact like before we disassemble |\tracingall|
 %    and reorder it partially).
 %    \begin{macrocode}
-  \def\tr@ce@n{%
-    \@tracingtrue
+  \edef\tr@ce@n{%
+    \noexpand\@tracingtrue
     \tracingstats\tw@
     \tracingpages\@ne
-    \tracinglostchars\@ne
+    \tracinglostchars\thr@@
     \tracingparagraphs\@ne
     \errorcontextlines\maxdimen
+    \ifdefined\tracingstacklevels \tracingstacklevels\maxdimen \fi
 %    \end{macrocode}
 %    We only change |\tracingoutput| if it hasn't already been enabled by
 %    |\showoutput|. If that's not the case, we set it to 2 so that we
@@ -512,12 +515,12 @@
 %  \changes{v1.1e}{2018/10/13}{Only reset \cs{tracingoutput} if not
 %    set by \cs{showoutput} earlier}
 %    \begin{macrocode}
-    \ifnum\tracingoutput=\@ne
-    \else
+    \noexpand\ifnum\tracingoutput=\@ne
+    \noexpand\else
       \tracingoutput\tw@
       \showboxbreadth\maxdimen
       \showboxdepth\maxdimen
-    \fi
+    \noexpand\fi
 %    \end{macrocode}
 %
 %    \begin{macrocode}
@@ -543,8 +546,11 @@
 %    |@tracing| switch and always set the primitives back to zero.
 %  \changes{v1.1c}{2003/04/30}{Turn off \cs{tracingoutput}}
 %  \changes{v1.1c}{2003/04/30}{Reset \cs{tracingstats} to one}
+%  \changes{v1.1f}{2021/04/18}{Add missing reset of \cs{errorcontextlines}}
+%  \changes{v1.1f}{2021/04/18}
+%                {Add \cs{tracingstacklevels} and \cs{tracinglostchars}=3}
 %    \begin{macrocode}
-  \def\conditionally@traceoff{%
+  \edef\conditionally@traceoff{%
     \tracingassigns\z@
     \tracingrestores\z@
     \tracingcommands\z@
@@ -557,15 +563,17 @@
 %  \changes{v1.1e}{2018/10/13}{Only reset \cs{tracingoutput} if not
 %    set by \cs{showoutput} earlier}
 %    \begin{macrocode}
-    \ifnum\tracingoutput=\tw@
+    \noexpand\ifnum\tracingoutput=\tw@
       \tracingoutput\z@
       \showboxbreadth\m@ne
       \showboxdepth\m@ne
-    \fi
+    \noexpand\fi
 %    \end{macrocode}
 %
 %    \begin{macrocode}
     \tracingstats\@ne
+    \ifdefined\tracingstacklevels \tracingstacklevels\z@ \fi
+    \errorcontextlines\m@ne
     \tracingparagraphs\z@
     \tracinggroups\z@
   }
-- 
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