path: root/Master/texmf-dist/source/latex/regexpatch/regexpatch.dtx

 % \iffalse meta-comment
%
%% File: regexpatch.dtx (C) Copyright 2012-2016 Enrico Gregorio
%%
%% 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
%%
%%    http://www.latex-project.org/lppl.txt
%%
%% This file is part of the "regexpatch bundle" (The Work in LPPL)
%% and all files in that bundle must be distributed together.
%%
%% The released version of this bundle is available from CTAN.
%%
%
%<*driver|package>
\RequirePackage{expl3}
%</driver|package>
%<*driver>
\expandafter\def\csname ver@thumbpdf.sty\endcsname{}
\documentclass[a4paper,full]{l3doc}
\usepackage{bookmark}
\newcommand{\sv}{[\texttt{*}]}
%</driver>
%<*driver|package>
\GetIdInfo$Id: regexpatch.dtx 0.2d 2018-05-02 12:00:00Z Enrico $
          {Extending etoolbox patching commands}
%</driver|package>
%<*driver>
\begin{document}
  \DocInput{\jobname.dtx}
\end{document}
%</driver>
% \fi
%
% \title{^^A
%   The \textsf{regexpatch} package^^A
%     \thanks{This file describes version \ExplFileVersion,
%     last revised \ExplFileDate.}^^A
%  \\ {\normalsize Replacing \textsf{etoolbox} patching
%   commands}^^A
% }
%
% \author{^^A
%  Enrico Gregorio\thanks
%    {^^A
%      E-mail:
%        Enrico DOT Gregorio AT univr DOT it^^A
%    }^^A
% }
%
% \date{Released \ExplFileDate}
%
% \maketitle
%
% \changes{v0.2d}{2018/05/02}{Fixed silly typo}
% \changes{v0.2c}{2018/03/31}{Removed loading of \texttt{l3regex}}
% \changes{v0.2b}{2016/05/15}{Fix for removed function}
% \changes{v0.2a}{2015/05/20}{Fixed silly mistake}
% \changes{v0.2}{2013/03/28}{Polished code and documentation}
% \changes{v0.2}{2013/03/28}{Additional biblatex related macros}
% \changes{v0.1c}{2013/03/25}{Replaced obsolete command
%   \texttt{\protect\string\protect\prg_case_str:onn}}
% \changes{v0.1c}{2013/03/25}{Replaced \texttt{\protect\string\protect\msg_term:x}
%    with \texttt{\protect\string\protect\msg_term:n}}
% \changes{v0.1b}{2012/07/24}{Fixed bugs in the `bibmacro' functions}
% \changes{v0.1a}{2012/06/07}{Fixed bugs in success/failure code}
% \changes{v0.1}{2012-04-15}{First public release}
% \begin{documentation}
%
% \begin{quotation}\small
% \begin{center}\bfseries\large
% Important preliminary notice
% \end{center}
% \medskip
%
% This is an experimental version and it might cease to work if the
% commands in the package \pkg{l3regex} are modified. When that
% \LaTeX3 package will be declared stable, this package will replace
% \pkg{xpatch} and calling |\usepackage{regexpatch}| will load the
% main package. Use at own risk.
% \end{quotation}
%
% \section{Introduction}
%
% The well known \pkg{etoolbox} package provides a bunch of functions
% for patching existing commands; in particular |\patchcmd|,
% |\pretocmd| and |\apptocmd| that do a wonderful job, but suffer from
% a limitation: if some package has defined
%\begin{verbatim}
% \newcommand{\xyz}[1][x]{-#1!}
%\end{verbatim}
% where |\xyz| has an optional argument, then |\patchcmd| and siblings
% cannot be used to modify the workings of |\xyz|. The same happens
% when a command has been defined with |\DeclareRobustCommand|.
%
% The reason for this is \TeX{}nical or, better, \LaTeX{}nical. When
% \LaTeX{} performs the above definition, the expansion of |\xyz| will
% be
%\begin{verbatim}
% \@protected@testopt \xyz \\xyz {x}
%\end{verbatim}
% where |\@protected@testopt| is a macro that essentially checks
% whether we are in a ``protected'' context, so that expansion should
% not be performed all the way (in moving arguments or write
% operations), or not; in the former case it issues a protected
% version of |\xyz|, while in the latter case it expands the macro
% |\\xyz| that is a \emph{single} command (yes, with a backslash in
% its name) which contains the real definition; a way to access this
% definition is to issue the command
%\begin{verbatim}
% \expandafter\show\csname\string\xyz\endcsname
%\end{verbatim}
% which will print in the log file the message
%\begin{verbatim}
% > \\xyz=\long macro:
% [#1]->-#1!.
%\end{verbatim}
% As usual, after |->| we see the definition. In order to use
% |\patchcmd| to change the exclamation mark into a hyphen one must do
%\begin{verbatim}
% \expandafter\patchcmd\csname\string\xyz\endcsname{!}{-}{}{}
%\end{verbatim}
% (see the documentation of \pkg{etoolbox} for details about the
% arguments).
%
% A similar situation happens if |\xyz| has been defined by
%\begin{verbatim}
% \DeclareRobustCommand{\xyz}{something}
%\end{verbatim}
% A |\show\xyz| instruction would show the cryptic
%\begin{verbatim}
% > \xyz=macro:
% ->\protect \xyz  .
%\end{verbatim}
% and only a close look reveals the clever trick used by the \LaTeX{}
% team: the |\protect| is not applied to |\xyz|, but to the macro
% \verb*?\xyz ? which has a space at the end of its name! And this
% macro is the one that contains the real definition. Indeed,
%\begin{verbatim}
% \expandafter\show\csname xyz\space\endcsname
%\end{verbatim}
% produces the message
%\begin{verbatim}
% > \xyz =\long macro:
% ->something.
%\end{verbatim}
% In this case, in order to apply |\patchcmd| we must say
%\begin{verbatim}
% \expandafter\patchcmd\csname xyz\space\endcsname{s}{S}{}{}
%\end{verbatim}
% If the macro with |\DeclareRobustCommand| is defined to have an
% optional argument, say
%\begin{verbatim}
% \DeclareRobustCommand{\xyz}[1][x]{-#1!}
%\end{verbatim}
% one has to combine the two tricks:
%\begin{verbatim}
% \expandafter\patchcmd\csname\string\xyz\space\endcsname{!}{-}{}{}
%\end{verbatim}
% It's hard and error prone to remember all of these tricks, so this
% package comes to the rescue.
%
% The package is now completely independent of \pkg{etoolbox}. It
% doesn't feature commands analogous to |\preto| and |\appto| that, in
% the author's opinion, are a bit dangerous, since somebody might
% apply them to commands defined with |\DeclareRobustCommand| or
% |\newrobustcmd|, with the obvious problems.
%
% The \pkg{regexpatch} package uses many features of the \LaTeX3
% experimental packages, in particular of \pkg{l3regex}. This has a
% clear advantage: we can have a *-variant of |\xpatchcmd| that does a
% ``replace~all'' which can avoid multiple uses of |\patchcmd| on the
% same macro. Moreover there's a very powerful |\regexpatchcmd|
% function that uses regular expression syntax for search and replace
% which can even patch commands defined under different category code
% setup.
%
% For example, let's see how the \LaTeX{} kernel defines |\strip@pt|:
%\begin{verbatim}
% \begingroup
%   \catcode`P=12
%   \catcode`T=12
%   \lowercase{
%     \def\x{\def\rem@pt##1.##2PT{##1\ifnum##2>\z@.##2\fi}}}
%   \expandafter\endgroup\x
% \def\strip@pt{\expandafter\rem@pt\the}
%\end{verbatim}
% The same result can be obtained by
%\begin{verbatim}
% \begingroup\def\defrem@pt{\endgroup
%   \def\rem@pt##1.##2pt{##1\ifnum##2>\z@.##2\fi}}
% \regexpatchcmd{\defrem@pt}{pt}{\cOp\cOt}{}{}
% \defrem@pt
% \def\strip@pt{\expandafter\rem@pt\the}
%\end{verbatim}
% Perhaps not so striking, but the pattern seems to be more intuitive;
% however the package supplies also a function for patching the
% parameter text of a macro:
%\begin{verbatim}
% \def\rem@pt#1.#2pt{#1\ifnum#2>\z@.#2\fi}
% \xpatchparametertext{\rem@pt}{pt}{\cO p \cO t}{}{}
%\end{verbatim}
% Of course, reading the manual of \pkg{l3regex} is necessary for
% being able to exploit the full power of |\regexpatchcmd| or
% |\xpatchparametertext|; in this case, `|\cO p|' (the space in between
% is optional) specifies a character `|p|' with category code `other'.
% Actually neither the |\cO| escape is necessary, as all letters in a
% replacement text in the context of regular expressions has category
% code 12 by default, but clarity is often to be preferred to
% efficiency.
%
%
% \section{Important notices}
%
% If the command to be patched contains `|@|-commands' in its
% replacement text, \emph{always} ensure that the patching code is
% enclosed between |\makeatletter| and |\makeatother|; this is
% different from what \pkg{etoolbox} requires. It's recommended to
% turn on |\tracingxpatches| when testing a patch, to get maximum
% information.
%
% Some people like to add informative messages to the \meta{failure}
% code in the patching commands. Usually I'm lazy and don't do it;
% when testing I find it better to trace the patchings or add |\ddt|
% to the \meta{failure} code. Adding warnings to the \meta{success}
% code is annoying for the user.
%
%
% \section{Acknowledgment}
%
% This package would not exist without the \pkg{l3regex} package
% and Bruno Le Floch. Some parts of \pkg{l3regex} were added just
% because I asked for them while developing the present package.
% Thanks also to Joseph Wright and all the \LaTeX3 team.
%
%
% \section{Commands}
%
% The main commands introduced by this package are
% \begin{itemize}
% \item |\xpretocmd|
% \item |\xapptocmd|
% \item |\xpatchcmd|
% \item |\regexpatchcmd|
% \end{itemize}
% which have the same syntax as the similar commands provided by
% \pkg{etoolbox} and apply to all kind of commands defined by
% \begin{itemize}
% \item the \LaTeX{} kernel macros |\newcommand|, |\renewcommand|,
% |\providecommand|, but also |\newenvironment| and
% |\renewenvironment|;
% \item the \LaTeX{} kernel macro for defining robust commands
% |\DeclareRobustCommand|;
% \item the \pkg{etoolbox} macros |\newrobustcmd|, |\renewrobustcmd|,
% |\providerobustcmd|.
% \end{itemize}
% Notice that patching the definition of the environment |foo|
% requires patching |\foo| or |\endfoo|.
%
% These commands will act as the original ones if the macro to patch
% is not robust or with optional arguments.
%
% There is also added functionality that \pkg{etoolbox} doesn't
% provide (at least easily for the first command):
% \begin{itemize}
% \item |\xpatchoptarg|
% \item |\xpatchparametertext|
% \item |\checkifpatchable|
% \end{itemize}
%
% Moreover the package defines
% \begin{itemize}
% \item |\xpretobibmacro|
% \item |\xapptobibmacro|
% \item |\xpatchbibmacro|
% \item |\regexpatchbibmacro|
% \end{itemize}
% that can be used to patch commands defined with \pkg{biblatex}'s
% |\newbibmacro|. Say that we have
%\begin{verbatim}
% \newbibmacro{foo.bar}[2]{#1 and #2}
%\end{verbatim}
% Then, to change |and| into |und|, we can now say
%\begin{verbatim}
% \xpatchbibmacro{foo.bar}{and}{und}{}{}
%\end{verbatim}
% \medskip
% \begin{lrbox}{0}
% \begin{minipage}{\dimexpr\textwidth-2\fboxsep-2\fboxrule\relax}
% \footnotesize^^A
% Patching these macros with \pkg{etoolbox} requires
% resorting to the \emph{very} cryptic
%\begin{verbatim}
% \expandafter\patchcmd\csname abx@macro@\detokenize{foo.bar}\endcsname
%   {and}{und}{}{}
%\end{verbatim}
% that would become an astonishing
%\begin{verbatim}
% \expandafter\patchcmd\csname\expandafter\string\csname
%   abx@macro@\detokenize{foo.bar}\endcsname\endcsname
%   {and}{und}{}{}
%\end{verbatim}
% if the original definition had been with an optional argument, say
%\begin{verbatim}
% \newbibmacro{foo.bar}[2][x]{#1 and #2}
%\end{verbatim}
% \end{minipage}
% \end{lrbox}
% \noindent\fbox{\usebox{0}}
%
% \medskip
%
% For \pkg{biblatex} users there are also
% \begin{itemize}
% \item |\xpretobibdriver|
% \item |\xapptobibdriver|
% \item |\xpatchbibdriver|
% \item |\regexpatchbibdriver|
% \end{itemize}
% for patching commands defined with |\DeclareBibliographyDriver|. One
% could use, for patching the driver |foo|,
%\begin{verbatim}
% \makeatletter
% \patchcmd{\blx@bbx@foo}{X}{Y}{success}{failure}
% \preto{\blx@bbx@foo}{P}
% \appto{\blx@bbx@foo}{A}
% \makeatother
%\end{verbatim}
% but having a lighter interface can be handy. Since our macros use
% |\pretocmd| and |\apptocmd| for consistency, remember to always use
% the |{success}| and |{failure}| arguments also with
% |\xpretobibdriver| and |\xapptobibdriver|.
%
% Under the same philosophy, one can use the macros
% \begin{itemize}
% \item |\xpatchfieldformat|,\\ |\xpretofieldformat|,\\ |\xapptofieldformat|,
% \item |\xpatchnameformat|,\\ |\xpretonameformat|,\\ |\xapptonameformat|,
% \item |\xpatchlistformat|,\\ |\xpretonameformat|,\\ |\xapptonameformat|,
% \item |\xpatchindexfieldformat|,\\ |\xpretoindexfieldformat|,\\ |\xapptoindexfieldformat|,
% \item |\xpatchindexnameformat|,\\ |\xpretoindexnameformat|,\\ |\xapptoindexnameformat|,
% \item |\xpatchindexlistformat|,\\ |\xpretoindexlistformat|,\\ |\xapptoindexlistformat|,
% \end{itemize}
% for the \pkg{biblatex} internal macro defined respectively with
% \begin{flushleft}
% |\DeclareFieldFormat|,
% |\DeclareNameFormat|,
% |\DeclareListFormat|,\\
% |\DeclareIndexFieldFormat|,
% |\DeclareIndexNameFormat|,
% |\DeclareIndexListFormat|.
% \end{flushleft}
% All the eighteen |\x...format| commands take a first optional argument, with
% default value |*|, see later on.
%
% Finally, the package defines the commands
% \begin{itemize}
% \item |\xshowcmd|
% \item |\xshowbibmacro|
% \item |\xshowbibdriver|
% \item |\xshowfieldformat|
% \item |\xshownameformat|
% \item |\xshowlistformat|
% \item |\xshowindexfieldformat|
% \item |\xshowindexnameformat|
% \item |\xshowindexlistformat|
% \item |\tracingxpatches|
% \end{itemize}
% The first three are the analog of |\show| to see the ``real''
% definition of a macro, be it defined with optional arguments or as a
% robust command; the |bib| ones are for the corresponding
% \pkg{biblatex} macros. The last one takes an optional argument for
% activating and deactivating the tracing system. So
%\begin{verbatim}
% \tracingxpatches
%\end{verbatim}
% will activate it (it's equivalent to |\tracingxpatches[1]|), while
%\begin{verbatim}
% \tracingxpatches[0]
%\end{verbatim}
% will stop issuing messages.
%
%
% \section{Syntax}
%
% Here is the formal syntax of the commands.
%
% \medskip
% {\small\noindent
% |\xpatchcmd|\marg{command}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\xpretocmd|\marg{command}\marg{prepend}^^A
%   \marg{success}\marg{failure}\\
% |\xapptocmd|\marg{command}\marg{append}^^A
%   \marg{success}\marg{failure}\\[\medskipamount]
% |\xpatchbibmacro|\marg{name}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\xpretobibmacro|\marg{name}\marg{prepend}^^A
%   \marg{success}\marg{failure}\\
% |\xapptobibmacro|\marg{name}\marg{append}^^A
%   \marg{success}\marg{failure}\\[\medskipamount]
% |\xpatchbibdriver|\marg{name}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\xpretobibdriver|\marg{name}\marg{prepend}^^A
%   \marg{success}\marg{failure}\\
% |\xapptobibdriver|\marg{name}\marg{append}^^A
%   \marg{success}\marg{failure}\\[\medskipamount]
% |\xpatchfieldformat|\oarg{entrytype}\marg{name}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\xpretofieldformat|\oarg{entrytype}\marg{name}\marg{prepend}^^A
%   \marg{success}\marg{failure}\\
% |\xapptofieldformat|\oarg{entrytype}\marg{name}\marg{append}^^A
%   \marg{success}\marg{failure}\\[\medskipamount]
% |\xpatchnameformat|\oarg{entrytype}\marg{name}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\xpretonameformat|\oarg{entrytype}\marg{name}\marg{prepend}^^A
%   \marg{success}\marg{failure}\\
% |\xapptonameformat|\oarg{entrytype}\marg{name}\marg{append}^^A
%   \marg{success}\marg{failure}\\[\medskipamount]
% |\xpatchlistformat|\oarg{entrytype}\marg{name}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\xpretolistformat|\oarg{entrytype}\marg{name}\marg{prepend}^^A
%   \marg{success}\marg{failure}\\
% |\xapptolistformat|\oarg{entrytype}\marg{name}\marg{append}^^A
%   \marg{success}\marg{failure}\\[\medskipamount]
% |\xpatchindexfieldformat|\oarg{entrytype}\marg{name}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\xpretoindexfieldformat|\oarg{entrytype}\marg{name}\marg{prepend}^^A
%   \marg{success}\marg{failure}\\
% |\xapptoindexfieldformat|\oarg{entrytype}\marg{name}\marg{append}^^A
%   \marg{success}\marg{failure}\\[\medskipamount]
% |\xpatchindexnameformat|\oarg{entrytype}\marg{name}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\xpretoindexnameformat|\oarg{entrytype}\marg{name}\marg{prepend}^^A
%   \marg{success}\marg{failure}\\
% |\xapptoindexnameformat|\oarg{entrytype}\marg{name}\marg{append}^^A
%   \marg{success}\marg{failure}\\[\medskipamount]
% |\xpatchindexlistformat|\oarg{entrytype}\marg{name}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\xpretoindexlistformat|\oarg{entrytype}\marg{name}\marg{prepend}^^A
%   \marg{success}\marg{failure}\\
% |\xapptoindexlistformat|\oarg{entrytype}\marg{name}\marg{append}^^A
%   \marg{success}\marg{failure}\\[\medskipamount]
% |\xshowcmd|\sv\marg{command}\\
% |\xshowbibname|\marg{name}\\
% |\xshowbibdriver|\marg{name}\\[\medskipamount]
% |\xpatchoptarg|\marg{name}\marg{replace}\\
% |\xpatchparametertext|\marg{name}\marg{search}\marg{replace}^^A
%   \marg{success}\marg{failure}\\
% |\checkifpatchable|\marg{name}\\
% |\tracingxpatches|\oarg{number}
%
% }
%
% \medskip
%
% \begingroup\emergencystretch=.5\textwidth
% Here \meta{command} is the command's name (with the backslash),
% while \meta{name} is the string that appears as the argument to
% |\newbibmacro|, |\DeclareBibliographyDriver|, |\DeclareFieldFormat|,
% |\DeclareNameFormat|, |\DeclareListFormat|, |\DeclareIndexFieldFormat|,
% |\DeclareIndexNameFormat| or |\DeclareIndexListFormat| respectively;
% \meta{search}, \meta{replace}, \meta{prepend} and \meta{append} are
% the list of tokens that are to be used for the specific tasks;
% \meta{success} and \meta{failure} are token lists to be executed if
% the patching succeeds or fails respectively. I find it useful to use
% |\ddt| as \meta{failure}, so that \TeX{} will stop for the undefined
% control sequence when the patching fails.\par\endgroup
%
% All the |\x...format| macros have an optional argument that by
% default is |*|.
%
% In the commands whose name contains the string |regex|, both
% \meta{search} and \meta{replace} are understood to represent regular
% expressions. Check with the documentation of \pkg{l3regex} for
% details.
%
% The *-variants of the |patch| type commands means that the
% replacement is performed on \emph{all} matches. With
% |\xshowcmd*\foo| one gets all information on |\foo|, as if the
% tracing system were activated, including the default optional
% argument, if existent. So it's best to use it before trying
% |\xpatchoptarg| (and all the other commands, of course).
%
% A curiosity about optional arguments: if one defines
%\begin{verbatim}
% \newcommand{\foo}[1][{bar}]{-#1-}
%\end{verbatim}
% then the braces around |bar| are stripped off. So with
%\begin{verbatim}
% \newcommand{\foo}[1][{\itshape bar}]{-#1-}
%\end{verbatim}
% all text following the call of |\foo| without an optional argument
% would be set in italics; one needs \emph{two} sets of braces, in
% this case. However,
%\begin{verbatim}
% \xpatchoptarg{\foo}{{\itshape bar}}
%\end{verbatim}
% would \emph{not} strip the braces.
%
% It's important to remember that patching commands that have |@| in
% their name must \emph{always} be performed between |\makeatletter|
% and |\makeatother|.
%
% \section{Examples}
%
% From \texttt{http://tex.stackexchange.com/a/42894}: the series
% of successive patches for changing the three occurrences of
% |\mathcode| in |\@addligto| into |\Umathcodenum| can become
%\begin{verbatim}
% \xpatchcmd*{\@addligto}{\mathcode}{\Umathcodenum}{}{}
%\end{verbatim}
% while the code
%\begin{verbatim}
% \expandafter\patchcmd\csname mathligsoff \endcsname
%   {\mathcode}{\Umathcodenum}{}{}
%\end{verbatim}
% needed without \pkg{regexpatch} can become
%\begin{verbatim}
% \xpatchcmd\mathligsoff{\mathcode}{\Umathcodenum}{}{}
%\end{verbatim}
%
% Another one: changing the space reserved for the theorem number in
% the `List of theorems' provided by \pkg{ntheorem} could be obtained
% with \pkg{etoolbox}'s |\patchcmd| by
%\begin{verbatim}
% \patchcmd{\thm@@thmline}{2.3em}{5em}{}{}
% \patchcmd{\thm@@thmline@name}{2.3em}{5em}{}{}
% \patchcmd{\thm@@thmline@noname}{2.3em}{5em}{}{}
%\end{verbatim}
% if the |hyperref| option is not used, but a long series of patches
% would be needed with the option, as |2.3em| appears three times in
% each macro. With \pkg{regexpatch} one can do independently of the
% option:
%\begin{verbatim}
% \xpatchcmd*{\thm@@thmline}{2.3em}{5em}{}{}
% \xpatchcmd*{\thm@@thmline@name}{2.3em}{5em}{}{}
% \xpatchcmd*{\thm@@thmline@noname}{2.3em}{5em}{}{}
%\end{verbatim}
%
% A user asked how to patch the |rubric| environment in the `CurVe'
% class in order to avoid the repetition of the rubric's title on
% continuation pages. The environment is based on |longtable| and the
% task is to remove the |\endhead| material, which is delimited by
% |\endfirsthead| and |\endhead|. Instead of
%\begin{verbatim}
% \patchcmd{\rubric}
%   {\endfirsthead\@rubrichead{#1\@continuedname}\\*[\rubricspace]\endhead}
%   {\endfirsthead}{}{}
%\end{verbatim}
% one can more simply exploit regular expressions:
%\begin{verbatim}
% \makeatletter % the replacement text has @-commands
% \regexpatchcmd{\rubric}
%   { \c{endfirsthead} .* \c{endhead} }
%   { \c{endfirsthead} }{}{}
% \makeatother
%\end{verbatim}
%
% Assume you want to insert a patch in the argument of a command; with
% the traditional method this is possible provided the patch text
% doesn't contain |#|. Here's an example
%\begin{verbatim}
% \makeatletter
% \usepackage{etoolbox} % for \ifdef
% \ifdef{\H@old@part}
%   {
%    \regexpatchcmd{\H@old@part}
%      {$} % regex representing the end
%      {\c{gdef}\c{cont@name@part}\cB\{\cP\#2\cE\}} % replacement
%      {}{}%
%   }
%   {
%    \regexpatchcmd{\@part}
%     {$}
%     {\c{gdef}\c{cont@name@part}\cB\{\cP\#2\cE\}}
%     {}{}%
%   }
% \makeatother
%\end{verbatim}
% We want to add |\gdef\cont@name@part{#2}| at the end of the
% replacement text, distinguishing when \pkg{hyperref} is loaded or
% not. So we patch the command by doing just what's requested. The
% example is a bit contrived, as using |\ifdefined| instead of the
% argument form wrapper would allow the traditional |\apptocmd|.
% However, other applications may be foreseen.
%
% A problem raised on |comp.text.tex| in 2008 was to extract the
% number from the name of the file being typeset; the name was of the
% form |lecture15.tex| and the question was how to define a macro
% |\lecturenumber| that acted on |\jobname| to do its work. The
% obvious
%\begin{verbatim}
% \def\lecturenumber{\expandafter\extractnumber\jobname;}
% \def\extractnumber lecture#1;{#1}
%\end{verbatim}
% doesn't work because the characters produced by |\jobname| all have
% category code 12 (spaces have 10, as usual). A nifty solution was
% provided by David Kastrup:
%\begin{verbatim}
% \begingroup
% \escapechar=-1
% \expandafter\endgroup
% \expandafter\def\expandafter\extractnumber\string\lecture#1;{#1}
%\end{verbatim}
% Now with |\xpatchparametertext| one can do
%\begin{verbatim}
% \def\lecturenumber{\expandafter\extractnumber\jobname;}
% \def\extractnumber lecture#1;{#1}
% \xpatchparametertext\extractnumber{lecture}{lecture}{}{}
%\end{verbatim}
% recalling that the substitution performed by \pkg{l3regex} uses
% category code 12 characters by default. The command can be
% generalized to accept any (fixed) prefix:
%\begin{verbatim}
% \def\setupfilenumber#1{%
%   \def\filenumber{\expandafter\extractnumber\jobname;}%
%   \def\extractnumber#1##1;{##1}%
%   \xpatchparametertext\extractnumber{#1}{#1}{}{}}
% \setupfilenumber{lecture}
%\end{verbatim}
% where the prefix is passed to |\setupfilenumber| and the macro to
% use is |\filenumber|.
%
% A proper \LaTeX3 definition might be
%\begin{verbatim}
% \NewDocumentCommand{\setupfilenumber}{ m }
%   {
%    \group_begin:
%    \cs_set:Npx \filenumber_aux:
%      {
%       \group_end:
%       \cs_set:Npn \exp_not:N \filenumber_extract:w
%         \tl_to_str:n { #1 } ####1 ; { ####1 }
%      }
%    \filenumber_aux:
%   }
% \NewDocumentCommand{\filenumber} {}
%   {
%    \exp_after:wN \filenumber_extract:w \c_job_name_tl ;
%   }
%\end{verbatim}
%
% \end{documentation}
%
% \begin{implementation}
%
% \section{The implementation of \pkg{regexpatch}}
%
% \iffalse
%<*package>
% \fi
%
% The usual starting stuff.
%    \begin{macrocode}
\ProvidesExplPackage
  {\ExplFileName}{\ExplFileDate}{\ExplFileVersion}{\ExplFileDescription}
\@ifpackagelater { expl3 } { 2012/01/19 }
  { }
  {
    \PackageError { regexpatch } { Support~package~l3kernel~too~old. }
      {
        Please~install~an~up~to~date~version~of~l3kernel~
        using~your~TeX~package~manager~or~from~CTAN.\\ \\
        Loading~regexpatch~will~abort!
      }
    \tex_endinput:D
  }
\RequirePackage{xparse}
%    \end{macrocode}
%
% \subsection{Variables}
%
% We define a bunch of variables: some booleans and token lists. The
% first tells us when the macro to patch has been defined by
% |\DeclareRobustCommand|, the second if it has an optional argument,
% the third if it's patchable, that is it can be reconstructed from
% its decomposition under the current category code regime. The last
% boolean is used for the tracing system: if true, messages about
% patching are issued.
%    \begin{macrocode}
\bool_new:N \l_xpatch_protect_bool
\bool_new:N \l_xpatch_optional_bool
\bool_new:N \l_xpatch_patchable_bool
\bool_new:N \l_xpatch_tracing_bool
%    \end{macrocode}
% The token list variables contain various items regarding the macro
% to patch: the name, the first level replacement text (we distinguish
% it from the `real' replacement text), the prefixes, the argument
% spec and the `real' replacement text.
%    \begin{macrocode}
\tl_new:N \l_xpatch_name_tl
\tl_new:N \l_xpatch_repl_tl
\tl_new:N \l_xpatch_prefix_tl
\tl_new:N \l_xpatch_arg_tl
\tl_new:N \l_xpatch_replacement_tl
\tl_new:N \l_xpatch_type_tl % for debugging messages
%    \end{macrocode}
% A variant for checking a regex match so that we can give the second
% argument as a token list.
%    \begin{macrocode}
\cs_generate_variant:Nn \regex_match:nnT {nV}
%    \end{macrocode}
%
% \subsection{Functions}
%
% The function |\xpatch_main_check:N| is responsible for telling us
% what kind of macro we're patching. Only one of the first four tests
% can be true; if none is, the macro is not `special' and can be
% patched without doing anything particular to get its
% `real~name'. The check consists in matching with a suitable regex
% at the start of the replacement text (which is in detokenized
% form). If the macro passes one of the first two tests, it can still
% have an optional argument, so a supplementary test is needed.
%
% Some technical remarks. Suppose we have the following definitions:
%\begin{verbatim}
% \DeclareRobustCommand{\xaa}[1]{xaa (DeclareRobustCommand-noopt)}
% \DeclareRobustCommand{\xab}[1][x]{xab (DeclareRobustCommand-opt)}
% \newcommand{\xac}[1][]{xac (newcommand-opt)}
% \newrobustcmd\xad[1][]{xad (newrobustcmd-opt)}
% \DeclareRobustCommand{\1}[1]{1 (DeclareRobustCommand-noopt)}
% \DeclareRobustCommand{\2}[1][]{2 (DeclareRobustCommand-opt)}
% \newcommand{\3}[1][]{3 (newcommand-opt)}
% \newrobustcmd\4[1][]{4 (newrobustcmd-opt)}
%\end{verbatim}
% Then the first level expansions are, respectively,
%\begin{verbatim*}
%+\protect \xaa  +
%+\protect \xab  +
%+\@protected@testopt \xac \\xac {}+
%+\@testopt \\xad {}+
%+\x@protect \1\protect \1  +
%+\x@protect \2\protect \2  +
%+\@protected@testopt \3\\3 {}+
%+\@testopt \\4 {}+
%\end{verbatim*}
% where the |+| is used to delimit the expansions and show the
% spaces. Remember that |\show| always adds a space after a control
% word, but not after a control symbol such as |\1|. However, in lines
% 5~and~6, \verb*?\1 ? is not a control symbol any more. So we have to
% take care of |\protect|, |\x@protect|, |\@protected@testopt| and
% |\@testopt|. But it's not simply sufficient to check for the
% presence of such a token at the start of the replacement text, or
% we'll be confused by macros such as |\linebreak|, whose replacement
% text starts with |\@testopt|. So we'll check also for the presence
% of the subsequent tokens, that depend on the macro's name. If the
% macro is recognized to have an optional argument, its default value
% is stored in |\tl_xpatch_repl_tl| (that we wouldn't use any more) to
% be shown by |\xshowcmd*| or when the tracing system is active: we
% throw away everything except what's contained between the final pair
% of braces.
%    \begin{macrocode}
\cs_new_protected:Npn \xpatch_main_check:N #1
  {
   \bool_set_false:N \l_xpatch_protect_bool
   \bool_set_false:N \l_xpatch_optional_bool
   \tl_set:Nx \l_xpatch_name_tl { \cs_to_str:N #1  }
   \tl_set:Nx \l_xpatch_repl_tl { \token_get_replacement_spec:N #1 }
   \tl_clear:N \l_xpatch_type_tl
   \regex_match:nVT % \DeclareRobustCommand<control word>
     {^\\protect\ \\\u{l_xpatch_name_tl}\ \ }
     \l_xpatch_repl_tl
     {
      \bool_set_true:N \l_xpatch_protect_bool
      \tl_put_right:Nx \l_xpatch_name_tl { \c_space_tl }
      \tl_set:Nn \l_xpatch_type_tl { DRCw }
     }
   \regex_match:nVT % \DeclareRobustCommand<control symbol>
     {^\\x@protect\ \\\u{l_xpatch_name_tl}\\}
     \l_xpatch_repl_tl
     {
      \bool_set_true:N \l_xpatch_protect_bool
      \tl_put_right:Nx \l_xpatch_name_tl { \c_space_tl }
      \tl_set:Nn \l_xpatch_type_tl { DRCs }
     }
   \regex_match:nVT % \newcommand<control word> with opt arg
     {^\\@protected@testopt\ \\\u{l_xpatch_name_tl}\ \\\\}
     \l_xpatch_repl_tl
     {
      \bool_set_true:N \l_xpatch_optional_bool
      \tl_put_left:Nx \l_xpatch_name_tl { \c_backslash_str }
      \tl_set:Nn \l_xpatch_type_tl { ncw+o }
     }
   \regex_match:nVT % \newcommand<control symbol> with opt arg
     {^\\@protected@testopt\ \\\u{l_xpatch_name_tl}\\\\}
     \l_xpatch_repl_tl
     {
      \bool_set_true:N \l_xpatch_optional_bool
      \tl_put_left:Nx \l_xpatch_name_tl { \c_backslash_str }
      \tl_set:Nn \l_xpatch_type_tl { ncs+o }
     }
   \regex_match:nVT % \newrobustcmd<any cs> with opt arg
     {^\\@testopt\ \\\\\u{l_xpatch_name_tl}}
     \l_xpatch_repl_tl
     {
      \bool_set_true:N \l_xpatch_optional_bool
      \tl_put_left:Nx \l_xpatch_name_tl { \c_backslash_str }
      \tl_set:Nn \l_xpatch_type_tl { nrc+o }
     }
   \bool_if:NT \l_xpatch_protect_bool
     {
      \tl_set:Nx \l_xpatch_repl_tl
        { \exp_after:wN \token_get_replacement_spec:N
            \cs:w \l_xpatch_name_tl \cs_end: }
      \regex_match:nVT % \DeclareRobustCommand<any cs> with opt arg
        {^\\@protected@testopt\ \\\u{l_xpatch_name_tl}\ \\\\}
        \l_xpatch_repl_tl
        {
         \bool_set_true:N \l_xpatch_optional_bool
         \tl_put_left:Nx \l_xpatch_name_tl { \c_backslash_str }
         \tl_put_right:Nn \l_xpatch_type_tl { +o }
        }
     }
   \bool_if:NT \l_xpatch_optional_bool
     {
      \regex_replace_once:nnN { .*? \{ (.*) \} \Z } { \1 }
        \l_xpatch_repl_tl
     }
  }
%    \end{macrocode}
% We use the information gathered with |\xpatch_main_check:N| to
% perform the patch; the macro to patch is |#2|, the function to
% execute is |#1|; in case the macro's name is misspelled, the
% following arguments will be ignored because they have already been
% absorbed. The main function is |\xpatch_main_four:NNnnnn|, where the
% |four| refers to the number of braced arguments for the |patch| and
% |regexpatch| type macros; we define also a |three| function for
% |preto| and |appto| macros, and a |zero| function for the |show|
% macros. We also define the variants taking a name as their second
% argument.
%    \begin{macrocode}
\cs_new_protected:Npn \xpatch_main_four:NNnnnn #1 #2 #3 #4 #5 #6
  {
   \cs_if_exist:NTF #2
     {
      \xpatch_main_check:N #2
      \bool_if:NT \l_xpatch_tracing_bool
        { \xpatch_message_cstype:N #2 }
      \exp_after:wN #1 \cs:w \l_xpatch_name_tl \cs_end: {#3}{#4}{#5}{#6}
     }
     {
      \msg_term:n
        {
         xpatch~message \\
        `\token_to_str:N #2'~is~undefined;~
        I'll~ignore~the~request.
        }
     }
  }
\cs_new_protected:Npn \xpatch_main_three:NNnnn #1 #2 #3 #4 #5
 {
  \xpatch_main_four:NNnnnn #1 #2 { #3 } { #4 } { #5 } { }
 }
\cs_new_protected:Npn \xpatch_main_zero:NN #1 #2
 {
  \xpatch_main_four:NNnnnn #1 #2 { } { } { } { }
 }
\cs_generate_variant:Nn \xpatch_main_zero:NN {Nc}
\cs_generate_variant:Nn \xpatch_main_three:NNnnn {Nc}
\cs_generate_variant:Nn \xpatch_main_four:NNnnnn {Nc}
%    \end{macrocode}
%
% Now we define the patching functions. We get all the parts in which
% a macro can be split: prefixes, parameter text and replacement text;
% the name is already available.  The token lists |\l_xpatch_X_tl|
% will contain the prefix or parameter text or replacement text of
% |#1| first in `detokenized' and then in `tokenized' form.
%    \begin{macrocode}
\cs_new_protected:Npn \xpatch_get_all:N #1
  {
   \tl_set:Nf \l_xpatch_prefix_tl { \token_get_prefix_spec:N #1 }
   \tl_set_rescan:Nnx \l_xpatch_prefix_tl { } \l_xpatch_prefix_tl
   \tl_set:Nf \l_xpatch_arg_tl { \token_get_arg_spec:N #1 }
   \tl_set_rescan:Nnx \l_xpatch_arg_tl { } \l_xpatch_arg_tl
   \tl_set:Nf \l_xpatch_replacement_tl { \token_get_replacement_spec:N #1 }
   \tl_set_rescan:Nnx \l_xpatch_replacement_tl { } \l_xpatch_replacement_tl
  }
%    \end{macrocode}
% After possible modifications to the replacement text, we can call
% |\xpatch_rebuild:N| to redo the definition of |#1|; we can also use
% it for checking if |#1| is patchable. Of course we need to use
% |\tex_def:D| at this point. Apologies to the developers of \LaTeX3
% that recommend never using |:D| functions.
%    \begin{macrocode}
\cs_new_protected:Npn \xpatch_rebuild:N #1
  {
   \use:x
     {
      \exp_not:V \l_xpatch_prefix_tl
      \tex_def:D % unavoidable
      \exp_not:N #1
      \exp_not:V \l_xpatch_arg_tl
      { \exp_not:V \l_xpatch_replacement_tl }
     }
  }
%    \end{macrocode}
% To check if |#1| is patchable, we rebuild it as |\xpatch_tmpa:w| and
% look whether |#1| and |\xpatch_tmpa:w| are the same. This is always
% the first thing to do, so we put |\xpatch_get_all:N| here; |#1| is
% the macro to patch.
%    \begin{macrocode}
\cs_new_protected:Npn \xpatch_check_patchable:N #1
  {
   \cs_if_exist:NTF #1
     {
      \xpatch_get_all:N #1
      \xpatch_rebuild:N \xpatch_tmpa:w
      \cs_if_eq:NNTF #1 \xpatch_tmpa:w
        {
         \bool_set_true:N \l_xpatch_patchable_bool
         \xpatch_message:n
           {
            Macro `\token_to_str:N #1'~is~patchable
           }
        }
        {
         \bool_set_false:N \l_xpatch_patchable_bool
         \xpatch_message:n
           {
            Macro `\token_to_str:N #1'~is~NOT~patchable\\
            (Check~if~it~contains~`@'~commands)
           }
        }
     }
     {
      \bool_set_false:N \l_xpatch_patchable_bool
      \xpatch_message:n
        {
         Macro `\token_to_str:N #1'~doesn't~exist.
        }
     }
  }
%    \end{macrocode}
%
% Defining the internal versions of |\xpretocmd| and |\xapptocmd| is
% easy: we check if the command is patchable and, if so, we prepend or append
% the second argument to the replacement text and rebuild the
% macro, then we execute the \meta{success} code. If the patch isn't
% possible we just execute the \meta{failure} code.
%    \begin{macrocode}
\cs_new_protected:Npn \xpatch_pretocmd:Nnnn #1 #2 #3 #4
  {
   \xpatch_check_patchable:N #1
   \bool_if:NTF \l_xpatch_patchable_bool
      {
       \tl_put_left:Nn \l_xpatch_replacement_tl { #2 }
       \xpatch_rebuild:N #1
       #3
      }
      {
       #4
      }
  }
\cs_new_protected:Npn \xpatch_apptocmd:Nnnn #1 #2 #3 #4
  {
   \xpatch_check_patchable:N #1
   \bool_if:NTF \l_xpatch_patchable_bool
      {
       \tl_put_right:Nn \l_xpatch_replacement_tl { #2 }
       \xpatch_rebuild:N #1
       #3
      }
      {
       #4
      }
  }
%    \end{macrocode}
%
% Substituting tokens in the replacement text is a bit harder, but not
% conceptually different. First the internal version of
% |\regexpatchcmd(*)|: check if |#1| is patchable, do the replacement
% if possible; beware that characters in the replacement string are of
% category 12 by default. We use |\regex_replace_all:nnNTF| and
% |\regex_replace_once:nnNTF| in order to pass correctly the success
% or failure arguments.
% \changes{v0.1a}{2012/06/07}{Fixed bugs in success/failure code with regex...nnNTF}
%    \begin{macrocode}
\cs_new_protected:Npn \xpatch_regexpatchcmd_all:Nnnnn #1 #2 #3 #4 #5
  {
   \xpatch_check_patchable:N #1
   \bool_if:NTF \l_xpatch_patchable_bool
      {
       \regex_replace_all:nnNTF { #2 } { #3 } \l_xpatch_replacement_tl
        { \xpatch_rebuild:N #1 #4 }
        { #5 }
      }
      {
       #5
      }
  }
\cs_new_protected:Npn \xpatch_regexpatchcmd_once:Nnnnn #1 #2 #3 #4 #5
  {
   \xpatch_check_patchable:N #1
   \bool_if:NTF \l_xpatch_patchable_bool
      {
       \regex_replace_once:nnNTF { #2 } { #3 } \l_xpatch_replacement_tl
        { \xpatch_rebuild:N #1 #4 }
        { #5 }
      }
      {
       #5
      }
  }
%    \end{macrocode}
%
% Thanks to the features of \pkg{l3regex}, we can also implement
% directly the analog of |\patchcmd|, but also with a `replace all'
% version.
%    \begin{macrocode}
\cs_new_protected:Npn \xpatch_patchcmd_once:Nnnnn #1 #2 #3 #4 #5
  {
   \xpatch_check_patchable:N #1
   \bool_if:NTF \l_xpatch_patchable_bool
      {
       \tl_set:Nn \l_tmpa_tl { #2 }
       \tl_set:Nn \l_tmpb_tl { #3 }
       \regex_replace_once:nnNTF
         { \u{l_tmpa_tl} }
         { \u{l_tmpb_tl} }
         \l_xpatch_replacement_tl
         { \xpatch_rebuild:N #1 #4 }
         { #5 }
      }
      {
       #5
      }
  }
\cs_new_protected:Npn \xpatch_patchcmd_all:Nnnnn #1 #2 #3 #4 #5
  {
   \xpatch_check_patchable:N #1
   \bool_if:NTF \l_xpatch_patchable_bool
      {
       \tl_set:Nn \l_tmpa_tl { #2 }
       \tl_set:Nn \l_tmpb_tl { #3 }
       \regex_replace_all:nnNTF
         { \u{l_tmpa_tl} }
         { \u{l_tmpb_tl} }
         \l_xpatch_replacement_tl
         { \xpatch_rebuild:N #1 #4 }
         { #5 }
      }
      {
       #5
      }
  }
%    \end{macrocode}
%
% Now the tracing system.
%    \begin{macrocode}
\cs_new_protected:Npn \xpatch_message:n #1
  {
   \bool_if:NT \l_xpatch_tracing_bool
     {
      \msg_term:n { xpatch~message \\ #1 }
     }
  }
\cs_new:Npn \xpatch_message_cstype:N #1
  {
   \str_case:onF { \l_xpatch_type_tl }
     {
      { DRCw }   {
                  \xpatch_message:n
                    {
                     `\token_to_str:N #1'~is~a~control~word~defined~
                     with~\token_to_str:N \DeclareRobustCommand
                    }
                 }
      { DRCw+o } {
                  \xpatch_message:n
                    {
                     `\token_to_str:N #1'~is~a~control~word~defined~
                     with~`\token_to_str:N \DeclareRobustCommand'~
                     and~a~default~optional~argument~`\l_xpatch_repl_tl'
                    }
                 }
      { DRCs }   {
                  \xpatch_message:n
                    {
                     `\token_to_str:N #1'~is~a~control~symbol~defined~
                     with~`\token_to_str:N \DeclareRobustCommand'
                    }
                 }
      { DRCs+o } {
                  \xpatch_message:n
                    {
                     `\token_to_str:N #1'~is~a~control~symbol~defined~
                     with~`\token_to_str:N \DeclareRobustCommand'~
                     and~a~default~optional~argument~`\l_xpatch_repl_tl'
                    }
                 }
      { ncw+o }  {
                  \xpatch_message:n
                    {
                     `\token_to_str:N #1'~is~a~control~word~defined~
                     with~`\token_to_str:N \newcommand'~
                     and~a~default~optional~argument~`\l_xpatch_repl_tl'
                    }
                 }
      { ncs+o }  {
                  \xpatch_message:n
                    {
                     `\token_to_str:N #1'~is~a~control~symbol~defined~
                     with~`\token_to_str:N \newcommand'~
                     and~a~default~optional~argument~`\l_xpatch_repl_tl'
                    }
                 }
      { nrc+o }  {
                  \xpatch_message:n
                    {
                     `\token_to_str:N #1'~is~a~control~sequence~defined~
                     with~`\token_to_str:N \newrobustcmd'~
                     and~a~default~optional~argument~`\l_xpatch_repl_tl'
                    }
                 }
      }
      {
       \xpatch_message:n
         {
          `\token_to_str:N #1'~is~not~especially~defined
         }
      }
  }
%    \end{macrocode}
%
% \subsection{The user level functions}
%
% Here are the functions for patching usual macros; the *-variants for
% |\xpatchcmd| and |\regexpatchcmd| do a `replace all'. All arguments
% are declared `long' with |+m| because we may need |\par| in them.
% \changes{v0.1a}{2012/06/07}{Fixed bug in success/failure code (missing final \texttt{n})}
%    \begin{macrocode}
\NewDocumentCommand{\xshowcmd} { s +m }
 {
  \IfBooleanT{#1}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
   }
  \xpatch_main_zero:NN \cs_show:N #2
  \IfBooleanT{#1}
   {
    \group_end:
   }
 }
\NewDocumentCommand{\xpretocmd}{ +m +m +m +m }
 { \xpatch_main_three:NNnnn \xpatch_pretocmd:Nnnn #1 {#2} {#3} {#4} }
\NewDocumentCommand{\xapptocmd}{ +m +m +m +m }
 { \xpatch_main_three:NNnnn \xpatch_apptocmd:Nnnn #1 {#2} {#3} {#4} }
\NewDocumentCommand{\regexpatchcmd}{ s +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   { \xpatch_main_four:NNnnnn \xpatch_regexpatchcmd_all:Nnnnn #2 {#3}{#4}{#5}{#6} }
   { \xpatch_main_four:NNnnnn \xpatch_regexpatchcmd_once:Nnnnn #2 {#3}{#4}{#5}{#6} }
 }
\NewDocumentCommand{\xpatchcmd}{ s +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   { \xpatch_main_four:NNnnnn \xpatch_patchcmd_all:Nnnnn #2 {#3}{#4}{#5}{#6} }
   { \xpatch_main_four:NNnnnn \xpatch_patchcmd_once:Nnnnn #2 {#3}{#4}{#5}{#6} }
 }
%    \end{macrocode}
%
% The functions for patching \pkg{biblatex} related macros that are
% given by name and we'll use the already defined variants.
%    \begin{macrocode}
\NewDocumentCommand{\xshowbibmacro} { s +m }
 {
  \IfBooleanT{#1}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
   }
  \xpatch_main_zero:Nc \cs_show:N { abx@macro@ \tl_to_str:n {#2} }
  \IfBooleanT{#1}
   {
    \group_end:
   }
 }
\NewDocumentCommand{\xpretobibmacro} { +m +m +m +m }
 {
  \xpatch_main_three:Ncnnn \xpatch_pretocmd:Nnnn
   { abx@macro@ \tl_to_str:n {#1} } {#2}{#3}{#4}
 }
\NewDocumentCommand{\xapptobibmacro} { +m +m +m +m }
 {
  \xpatch_main_three:Ncnnn \xpatch_apptocmd:Nnnn
   { abx@macro@ \tl_to_str:n {#1} } {#2}{#3}{#4}
 }
\NewDocumentCommand{\xpatchbibmacro} { s +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_all:Nnnnn
     { abx@macro@ \tl_to_str:n {#2} } {#3}{#4}{#5}{#6}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_once:Nnnnn
     { abx@macro@ \tl_to_str:n {#2} } {#3}{#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\regexpatchbibmacro} { s +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_all:Nnnnn
     { abx@macro@ \tl_to_str:n {#2} } {#3}{#4}{#5}{#6}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_once:Nnnnn
     { abx@macro@ \tl_to_str:n {#2} } {#3}{#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xshowbibdriver} { s +m }
 {
  \IfBooleanT{#1}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
   }
  \xpatch_main_zero:Nc \cs_show:N { blx@bbx@#2 }
  \IfBooleanT{#1}
   {
    \group_end:
   }
 }
\NewDocumentCommand{\xpretobibdriver} { +m +m +m +m }
 { \exp_args:Nc \xpatch_pretocmd:Nnnn {blx@bbx@#1} {#2}{#3}{#4} }
\NewDocumentCommand{\xapptobibdriver} { +m +m +m +m }
 { \exp_args:Nc \xpatch_apptocmd:Nnnn {blx@bbx@#1} {#2}{#3}{#4} }
\NewDocumentCommand{\xpatchbibdriver} { s +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   { \exp_args:Nc \xpatch_patchcmd_all:Nnnnn {blx@bbx@#2} {#3}{#4}{#5}{#6} }
   { \exp_args:Nc \xpatch_patchcmd_once:Nnnnn {blx@bbx@#2} {#3}{#4}{#5}{#6} }
 }
\NewDocumentCommand{\regexpatchbibdriver} { s +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   { \exp_args:Nc \xpatch_regexpatchcmd_all:Nnnnn {blx@bbx@#2} {#3}{#4}{#5}{#6} }
   { \exp_args:Nc \xpatch_regexpatchcmd_once:Nnnnn {blx@bbx@#2} {#3}{#4}{#5}{#6} }
 }
%    \end{macrocode}
% \changes{v0.2c}{2018/03/31}{Fixed wrong function name in \texttt{\protect\string\protect\xpatchbibmacro}}
% \changes{v0.2a}{2015/05/20}{Fixed silly mistake}
% Other \pkg{biblatex} related macros, added by request of the
% maintainers.
% \changes{v0.2}{2013/03/28}{Additional biblatex related macros}
%    \begin{macrocode}
\NewDocumentCommand{\xshowfieldformat} { s O{*} +m }
 {
  \IfBooleanT{#1}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
   }
  \xpatch_main_zero:Nc \cs_show:N { abx@ffd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} }
  \IfBooleanT{#1}
   {
    \group_end:
   }
 }
\NewDocumentCommand{\xpretofieldformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_all:Nnnn
     { abx@ffd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_once:Nnnn
     { abx@ffd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xapptofieldformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_all:Nnnn
     { abx@ffd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_once:Nnnn
     { abx@ffd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xpatchfieldformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_all:Nnnnn
     { abx@ffd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_once:Nnnnn
     { abx@ffd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }
\NewDocumentCommand{\regexpatchfieldformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_all:Nnnnn
     { abx@ffd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_once:Nnnnn
     { abx@ffd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }

\NewDocumentCommand{\xshownameformat} { s O{*} +m }
 {
  \IfBooleanT{#1}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
   }
  \xpatch_main_zero:Nc \cs_show:N { abx@nfd@ \tl_to_str:n {#1} @ \tl_to_str:n {#2} }
  \IfBooleanT{#1}
   {
    \group_end:
   }
 }
\NewDocumentCommand{\xpretonameformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_all:Nnnn
     { abx@nfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_once:Nnnn
     { abx@nfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xapptonameformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
   \xpatch_main_three:Ncnnn \xpatch_apptocmd_all:Nnnn
     { abx@nfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_once:Nnnn
     { abx@nfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xpatchnameformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_all:Nnnnn
     { abx@nfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_once:Nnnnn
     { abx@nfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }
\NewDocumentCommand{\regexpatchnameformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_all:Nnnnn
     { abx@nfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_once:Nnnnn
     { abx@nfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }

\NewDocumentCommand{\xshowlistformat} { s O{*} +m }
 {
  \IfBooleanT{#1}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
   }
  \xpatch_main_zero:Nc \cs_show:N { abx@lfd@ \tl_to_str:n {#1} @ \tl_to_str:n {#2} }
  \IfBooleanT{#1}
   {
    \group_end:
   }
 }
\NewDocumentCommand{\xpretolistformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_all:Nnnn
     { abx@lfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_once:Nnnn
     { abx@lfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xapptolistformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_all:Nnnn
     { abx@lfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_once:Nnnn
     { abx@lfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xpatchlistformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_all:Nnnnn
     { abx@lfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_once:Nnnnn
     { abx@lfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }
\NewDocumentCommand{\regexpatchlistformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_all:Nnnnn
     { abx@lfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_once:Nnnnn
     { abx@lfd@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }

\NewDocumentCommand{\xshowindexfieldformat} { s O{*} +m }
 {
  \IfBooleanT{#1}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
   }
  \xpatch_main_zero:Nc \cs_show:N { abx@fid@ \tl_to_str:n {#1} @ \tl_to_str:n {#2} }
  \IfBooleanT{#1}
   {
    \group_end:
   }
 }
\NewDocumentCommand{\xpretoindexfieldformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_all:Nnnn
     { abx@fid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_once:Nnnn
     { abx@fid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xapptoindexfieldformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_all:Nnnn
     { abx@fid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_once:Nnnn
     { abx@fid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xpatchindexfieldformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_all:Nnnnn
     { abx@fid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_once:Nnnnn
     { abx@fid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }
\NewDocumentCommand{\regexpatchindexfieldformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_all:Nnnnn
     { abx@fid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_once:Nnnnn
     { abx@fid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }

\NewDocumentCommand{\xshowindexnameformat} { s O{*} +m }
 {
  \IfBooleanT{#1}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
   }
  \xpatch_main_zero:Nc \cs_show:N { abx@nid@ \tl_to_str:n {#1} @ \tl_to_str:n {#2} }
  \IfBooleanT{#1}
   {
    \group_end:
   }
 }
\NewDocumentCommand{\xpretoindexnameformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_all:Nnnn
     { abx@nid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_once:Nnnn
     { abx@nid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xapptoindexnameformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_all:Nnnn
     { abx@nid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_once:Nnnn
     { abx@nid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xpatchindexnameformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_all:Nnnnn
     { abx@nid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_once:Nnnnn
     { abx@nid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }
\NewDocumentCommand{\regexpatchindexnameformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_all:Nnnnn
     { abx@nid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_once:Nnnnn
     { abx@nid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }

\NewDocumentCommand{\xshowindexlistformat} { s O{*} +m }
 {
  \IfBooleanT{#1}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
   }
  \xpatch_main_zero:Nc \cs_show:N { abx@lid@ \tl_to_str:n {#1} @ \tl_to_str:n {#2} }
  \IfBooleanT{#1}
   {
    \group_end:
   }
 }
\NewDocumentCommand{\xpretoindexlistformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_all:Nnnn
     { abx@lid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_pretocmd_once:Nnnn
     { abx@lid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xapptoindexlistformat} { s O{*} +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_all:Nnnn
     { abx@lid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
   {
    \xpatch_main_three:Ncnnn \xpatch_apptocmd_once:Nnnn
     { abx@lid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}
   }
 }
\NewDocumentCommand{\xpatchindexlistformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_all:Nnnnn
     { abx@lid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_patchcmd_once:Nnnnn
     { abx@lid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }
\NewDocumentCommand{\regexpatchindexlistformat} { s O{*} +m +m +m +m +m }
 {
  \IfBooleanTF{#1}
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_all:Nnnnn
     { abx@lid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
   {
    \xpatch_main_four:Ncnnnn \xpatch_regexpatchcmd_once:Nnnnn
     { abx@lid@ \tl_to_str:n {#2} @ \tl_to_str:n {#3} } {#4}{#5}{#6}{#7}
   }
 }
%    \end{macrocode}
% A macro to check if the macro is patchable. It just prints a message
% on the terminal and in the log file.
%    \begin{macrocode}
\NewDocumentCommand{\checkpatchable}{ +m }
 {
  \group_begin:
  \bool_set_true:N \l_xpatch_tracing_bool
  \xpatch_check_patchable:N #1
  \group_end:
 }
%    \end{macrocode}
% The last user level command: a macro for changing the optional
% argument in a macro that has one.
%    \begin{macrocode}
\cs_generate_variant:Nn \xpatch_get_all:N {c}
\cs_generate_variant:Nn \xpatch_rebuild:N {c}
\NewDocumentCommand{\xpatchoptarg}{ +m +m }
 {
  \xpatch_main_check:N #1
  \bool_if:NTF \l_xpatch_optional_bool
   {
%    \end{macrocode}
% We have a macro with optional argument; so we strip off
% the first backslash from the name and proceed.
%    \begin{macrocode}
    \tl_set:Nx \l_xpatch_name_tl { \tl_tail:V \l_xpatch_name_tl }
%    \end{macrocode}
% Gather the prefix (it is |\protected| when |#1| has been defined
% with |\newrobustcmd|).
%    \begin{macrocode}
    \tl_set:Nf \l_xpatch_prefix_tl { \token_get_prefix_spec:N #1 }
    \tl_clear:N \l_xpatch_prefix_tl
    \tl_set_rescan:Nnx \l_xpatch_prefix_tl { } \l_xpatch_prefix_tl
%    \end{macrocode}
% Get the replacement text in tokenized form: the control sequences
% have spaces in their names, so we can't rely on
% |\token_get_replacement_spec:N| because the spaces would be lost.
%    \begin{macrocode}
    \tl_set_eq:Nc \l_xpatch_replacement_tl { \l_xpatch_name_tl }
%    \end{macrocode}
% Now we have to change the last item in the token list: we just store
% the new optional argument in a token list variable and do a regex
% substitution, based on the fact that the replacement text consists
% of control sequences, an open brace, the optional argument and a
% closed brace, so we anchor at the end of the token list.
%    \begin{macrocode}
    \tl_set:Nn \l_tmpa_tl { { #2 } }
    \regex_replace_once:nnN { \cB. .* \cE. \Z} { \u{l_tmpa_tl} }
     \l_xpatch_replacement_tl
%    \end{macrocode}
% Now we rebuild the control sequence.
%    \begin{macrocode}
    \xpatch_rebuild:c { \l_xpatch_name_tl }
   }
%    \end{macrocode}
% If the macro hasn't an optional argument we issue a message.
%    \begin{macrocode}
   {
    \group_begin:
    \bool_set_true:N \l_xpatch_tracing_bool
    \xpatch_message:n
     {
      Macro~`\token_to_str:N #1'~ has~no~optional~argument~
      or~it~has~been~defined~with~`xparse'~and~operating~
      on~such~commands~is~(still)~not~supported
     }
    \group_end:
   }
 }
%    \end{macrocode}
% Just one more thing: enabling or disabling the tracing system.
%    \begin{macrocode}
\NewDocumentCommand{\tracingxpatches}{ O{1} }
 {
  \int_compare:nTF { #1 > 0 }
   { \bool_set_true:N \l_xpatch_tracing_bool }
   { \bool_set_false:N \l_xpatch_tracing_bool }
 }
%    \end{macrocode}
% One more thing: patching the parameter text!
%    \begin{macrocode}
\NewDocumentCommand{\xpatchparametertext}{ +m +m +m +m +m }
 {
  \xpatch_check_patchable:N #1
  \bool_if:NTF \l_xpatch_patchable_bool
   {
    \regex_replace_once:nnN { #2 } { #3 } \l_xpatch_arg_tl
    \xpatch_rebuild:N #1
    #4
   }
   {
    #5
   }
 }
%    \end{macrocode}
%
% \iffalse
%</package>
% \fi
% \end{implementation}
%
% \PrintIndex
% \PrintChanges