From d08faae51fbb21827ca2fe7b782112631fff7b53 Mon Sep 17 00:00:00 2001
From: Karl Berry <karl@freefriends.org>
Date: Sun, 12 Aug 2018 21:56:33 +0000
Subject: nicematrix (12aug18)

git-svn-id: svn://tug.org/texlive/trunk@48395 c570f23f-e606-0410-a88d-b1316a301751
---
 .../source/latex/nicematrix/nicematrix.dtx         | 2811 +++++++++++++-------
 1 file changed, 1863 insertions(+), 948 deletions(-)

(limited to 'Master/texmf-dist/source/latex/nicematrix/nicematrix.dtx')

diff --git a/Master/texmf-dist/source/latex/nicematrix/nicematrix.dtx b/Master/texmf-dist/source/latex/nicematrix/nicematrix.dtx
index 18b1e89ad3a..753cebb6e9b 100644
--- a/Master/texmf-dist/source/latex/nicematrix/nicematrix.dtx
+++ b/Master/texmf-dist/source/latex/nicematrix/nicematrix.dtx
@@ -1,6 +1,6 @@
 % \iffalse meta-comment
 %
-% Copyright (C) 2017 by F. Pantigny
+% Copyright (C) 2017-2018 by F. Pantigny
 % -----------------------------------
 %
 % This file may be distributed and/or modified under the
@@ -15,8 +15,8 @@
 %
 % \fi
 % \iffalse
-\def\myfileversion{2.0}
-\def\myfiledate{2018/07/06}
+\def\myfileversion{2.1}
+\def\myfiledate{2018/08/12}
 %
 %
 %<*batchfile>
@@ -44,7 +44,7 @@ version 2005/12/01 or later.
 \endgroup
 %</batchfile>
 %
-%<@@=nicem>
+%<@@=nm>
 %<*driver>
 \documentclass[dvipsnames]{l3doc}% dvipsnames is for xcolor (loaded by Tikz, loaded by nicematrix)
 \VerbatimFootnotes
@@ -62,7 +62,10 @@ version 2005/12/01 or later.
 \titlespacing*{\subsection}{0pt}{4.5ex plus 1ex minus .2ex}{2ex plus .2ex}
 \usepackage{multicol}
 \setlength{\columnseprule}{0.4pt}
+\usepackage{colortbl}
+\usepackage{arydshln}
 \parindent 0pt
+
 \DisableCrossrefs
 \begin{document}
 \DocInput{nicematrix.dtx}
@@ -87,12 +90,9 @@ version 2005/12/01 or later.
 %
 % This package can be used with |xelatex|, |lualatex|, |pdflatex| but also by the classical workflow
 % |latex|-|dvips|-|ps2pdf| (or Adobe Distiller). Two or three compilations may be necessary. This package requires
-% and loads the packages \pkg{expl3}, \pkg{l3keys2e}, \pkg{xparse}, \pkg{array}, \pkg{mathtools} and \pkg{tikz}.
+% and loads the packages \pkg{expl3}, \pkg{l3keys2e}, \pkg{xparse}, \pkg{array}, \pkg{amsmath} and \pkg{tikz}. It
+% also loads the Tikz library \pkg{fit}.
 %
-% \tikzset{highlight/.style={rectangle,
-%                            fill=red!15,
-%                            blend mode = multiply,
-%                            inner sep=1pt}}
 %
 %
 % \medskip
@@ -110,14 +110,12 @@ version 2005/12/01 or later.
 %  \begin{bNiceArrayRC}{CCCC}%
 %                            [code-for-last-col=\color{blue}\scriptstyle,
 %                             code-for-first-row=\color{blue}\scriptstyle,
-%                             code-after = {\tikz \node [highlight,fit = (0-1) (0-4)] {};
-%                                           \tikz \node [highlight,fit = (1-5) (4-5)] {};},
 %                             columns-width = auto]
 % C_1     & C_2     & \Cdots  & C_n  \\
 % a_{11}  & a_{12}  & \Cdots & a_{1n}  & L_1 \\
 % a_{21}  & a_{22}  & \Cdots & a_{2n}  & L_2 \\
 % \Vdots & \Vdots & \Ddots & \Vdots & \Vdots \\
-% a_{n1}  & a_{n2}  & \Cdots & a_{nn}  & L_n \\
+% a_{n1}  & a_{n2}  & \Cdots & a_{nn}  & L_n 
 % \end{bNiceArrayRC}
 % }$
 % 
@@ -131,8 +129,7 @@ version 2005/12/01 or later.
 %
 % \medskip
 % \begin{minipage}{10cm}
-% For example, consider the following code which uses an environment |{pmatrix}| of \pkg{amsmath} (or
-% \pkg{mathtools}).
+% For example, consider the following code which uses an environment |{pmatrix}| of \pkg{amsmath}.
 %
 % \smallskip
 % \begin{BVerbatim}
@@ -169,7 +166,6 @@ version 2005/12/01 or later.
 % 0      & \cdots & 0      & 1
 % \end{pmatrix}$
 % \end{scope}
-% 
 %
 %
 % \section{The environments of this extension} 
@@ -192,8 +188,8 @@ version 2005/12/01 or later.
 %
 % \medskip
 % By default, the environments |{NiceMatrix}|, |{pNiceMatrix}|, |{bNiceMatrix}|, |{BNiceMatrix}|, |{vNiceMatrix}|
-% and |{VNiceMatrix}| behave almost exactly as the corresponding environments of \pkg{amsmath} (and
-% \pkg{mathtools}): |{matrix}|, |{pmatrix}|, |{bmatrix}|, |{Bmatrix}|, |{vmatrix}| and |{Vmatrix}|.
+% and |{VNiceMatrix}| behave almost exactly as the corresponding environments of \pkg{amsmath}:
+% |{matrix}|, |{pmatrix}|, |{bmatrix}|, |{Bmatrix}|, |{vmatrix}| and |{Vmatrix}|.
 % 
 %
 % \medskip
@@ -284,7 +280,8 @@ version 2005/12/01 or later.
 % 
 % \bigskip
 % In the first column of this exemple, there are two instructions |\Vdots| but only one dotted line is drawn (there
-% is no overlapping graphic objects in the resulting \textsc{pdf}).
+% is no overlapping graphic objects in the resulting \textsc{pdf}\footnote{And it's not possible to draw a |\Ldots|
+% and a |\Cdots| line between the same cells.}).
 %
 % However, useless computations are performed by TeX before detecting that both instructions would eventually yield
 % the same dotted line. That's why the package \pkg{nicematrix} provides starred versions of |\Ldots|, |\Cdots|,
@@ -353,7 +350,7 @@ version 2005/12/01 or later.
 %
 % Consider the following matrix composed classicaly with the environment |{pmatrix}|.\par\nobreak
 % \medskip
-% \begin{BVerbatim}[baseline=c,boxwidth=7cm]
+% \begin{BVerbatim}[baseline=c,boxwidth=8cm]
 % $A = \begin{pmatrix}
 % a_0 & b \\
 % a_1 &   \\
@@ -376,7 +373,7 @@ version 2005/12/01 or later.
 % \bigskip
 % If we add |\vdots| instructions in the second column, the geometry of the matrix is modified.\par\nobreak
 % \medskip
-% \begin{BVerbatim}[baseline=c,boxwidth=7cm]
+% \begin{BVerbatim}[baseline=c,boxwidth=8cm]
 % $B = \begin{pmatrix}
 % a_0 & b      \\
 % a_1 & \vdots \\
@@ -399,7 +396,7 @@ version 2005/12/01 or later.
 % By default, with \pkg{nicematrix}, if we replace |{pmatrix}| by |{pNiceMatrix}| and |\vdots| by
 % |\Vdots| (or |\Vdots*| for efficiency), the geometry of the matrix is not changed.\par\nobreak
 % \medskip
-% \begin{BVerbatim}[baseline=c,boxwidth=7cm]
+% \begin{BVerbatim}[baseline=c,boxwidth=8cm]
 % $C = \begin{pNiceMatrix}
 % a_0 & b       \\
 % a_1 & \Vdots  \\
@@ -423,7 +420,7 @@ version 2005/12/01 or later.
 % line in the second column. It's possible by using the option |nullify-dots| (and only one instruction |\Vdots| is
 % necessary).\par\nobreak
 % \medskip
-% \begin{BVerbatim}[baseline=c,boxwidth=7cm]
+% \begin{BVerbatim}[baseline=c,boxwidth=8cm]
 % $D = \begin{pNiceMatrix}[~emphase#nullify-dots@]
 % a_0 & b      \\
 % a_1 & \Vdots \\
@@ -449,10 +446,11 @@ version 2005/12/01 or later.
 % \subsection{The command Hdotsfor}
 %
 % Some people commonly use the command |\hdotsfor| of \pkg{amsmath} in order to draw horizontal dotted lines in a
-% matrix. In the environments of \pkg{nicematrix}, they should use instead the command |\Hdotsfor| and they will
-% have the same style of dotted lines. We recommand not to use this command in new code since it's more coherent to
-% use exclusively |\Cdots|, |\Vdots|, |\Ddots|, etc. However, it can be useful in adapting existing code,
-% especially when using the option |transparent| (see below).
+% matrix. In the environments of \pkg{nicematrix}, one should use instead |\Hdotsfor| in order to draw dotted lines similar
+% to the other dotted lines drawn by the package \pkg{nicematrix}.
+%
+% As with the other commands of \pkg{nicematrix} (like |\Cdots|, |\Ldots|, |\Vdots|, etc.), the dotted line drawn
+% with |\Hdotsfor| extends until the contents of the cells on both sides.
 %
 % \medskip
 % \begin{BVerbatim}[baseline=c,boxwidth=7cm]
@@ -470,9 +468,29 @@ version 2005/12/01 or later.
 % 1 & 2 & 3 & 4 & 5 \\
 % \end{pNiceMatrix}$
 %
+% \bigskip
+% However, if these cells are empty, the dotted line extends only in the cells specified by the argument of
+% |\Hdotsfor| (by design).
+%
 % \medskip
+% \begin{BVerbatim}[baseline=c,boxwidth=7cm]
+% $\begin{pNiceMatrix}
+% 1 & 2 & 3 & 4 & 5 \\
+%   & ~emphase#\Hdotsfor{3}@ \\
+% 1 & 2 & 3 & 4 & 5 \\
+% 1 & 2 & 3 & 4 & 5 \\
+% \end{pNiceMatrix}$
+% \end{BVerbatim}
+% $\begin{pNiceMatrix}
+% 1 & 2 & 3 & 4 & 5 \\
+%   & \Hdotsfor{3} \\
+% 1 & 2 & 3 & 4 & 5 \\
+% 1 & 2 & 3 & 4 & 5 \\
+% \end{pNiceMatrix}$
+%
+% \bigskip
 % The command |\hdotsfor| of \pkg{amsmath} takes an optional argument (between square brackets) which is 
-% used for fine tuning of the space beetween two consecutive dots. For homogeneity, the command |\Hdotsfor| has
+% used for fine tuning of the space beetween two consecutive dots. For homogeneity, |\Hdotsfor| has
 % also an optional argument but this argument is discarded silently.
 % 
 % \subsection{How to generate the continuous dotted lines transparently}
@@ -492,7 +510,7 @@ version 2005/12/01 or later.
 % |\iddots| is not a command of LaTeX but is defined by the package \pkg{nicematrix}. If |mathdots| is loaded, the
 % version of |mathdots| is used.} and |\hdotsfor| are redefined within the environments provided by \pkg{nicematrix} 
 % and behave like |\Ldots|, |\Cdots|, |\Vdots|, |\Ddots|, |\Iddots| and |\Hdotsfor|; the command |\dots| (``automatic
-% dots'' of |amsmath| --- and |mathtools|) is also redefined to behave like |\Ldots|.
+% dots'' of |amsmath|) is also redefined to behave like |\Ldots|.
 %
 % \item  The option |renew-matrix|\par\nobreak
 % With this option, the environment |{matrix}| is redefined and behave like |{NiceMatrix}|, and so on for the five
@@ -520,122 +538,6 @@ version 2005/12/01 or later.
 % 0      & \cdots & 0      & 1
 % \end{pmatrix}$
 % \end{scope}
-%
-% \section{The width of the columns}
-% \label{width}
-%
-% In the environments with an explicit preamble (like |{NiceArray}|, |{pNiceArrayC}|, etc.), It's possible to fix the
-% width of a given column with the standard letters |w| and |W| of the package \pkg{array}.
-% 
-% \medskip
-% \begin{BVerbatim}[baseline=c,boxwidth=10cm]
-% $\left(\begin{NiceArray}{~emphase#wc{1cm}@CC}
-% 1  & 12 & -123 \\
-% 12 & 0  & 0    \\
-% 4  & 1  & 2 
-% \end{NiceArray}\right)$
-% \end{BVerbatim}
-% $\left(\begin{NiceArray}{wc{1cm}CC}
-% 1  & 12 & -123 \\
-% 12 & 0  & 0    \\
-% 4  & 1  & 2 
-% \end{NiceArray}\right)$
-%
-%
-% \bigskip
-% It's also possible to fix the width of all the columns of a matrix directly with the option |columns-width| (in
-% all the environments of \pkg{nicematrix}).
-% 
-% \medskip
-% \begin{BVerbatim}[baseline=c,boxwidth=10cm]
-% $\begin{pNiceMatrix}[~emphase#columns-width = 1cm@]
-% 1  & 12 & -123 \\
-% 12 & 0  & 0    \\
-% 4  & 1  & 2 
-% \end{pNiceMatrix}$
-% \end{BVerbatim}
-% $\begin{pNiceMatrix}[columns-width = 1cm]
-% 1  & 12 & -123 \\
-% 12 & 0  & 0    \\
-% 4  & 1  & 2 
-% \end{pNiceMatrix}$
-%
-% \medskip
-% Note that the space inserted between two columns (equal to 2 |\arraycolsep|) is not suppressed.
-%
-% \bigskip
-% It's possible to give the value |auto| to the option |columns-width|: all the columns of the array will
-% have a width equal to the widest cell of the array. \textbf{Two or three compilations may be necessary.}\par\nobreak
-% \medskip
-% \begin{BVerbatim}[baseline=c,boxwidth=10cm]
-% $\begin{pNiceMatrix}[~emphase#columns-width = auto@]
-% 1  & 12 & -123 \\
-% 12 & 0  & 0    \\
-% 4  & 1  & 2 
-% \end{pNiceMatrix}$
-% \end{BVerbatim}
-% $\begin{pNiceMatrix}[columns-width = auto]
-% 1  & 12 & -123 \\
-% 12 & 0  & 0    \\
-% 4  & 1  & 2 
-% \end{pNiceMatrix}$
-% 
-% \bigskip
-% It's possible to fix the width of the columns of all the matrices of a current scope with the command
-% |\NiceMatrixOptions|.\par\nobreak 
-% \medskip
-% \begin{BVerbatim}[baseline=c,boxwidth=8.5cm]
-% ~emphase#\NiceMatrixOptions{columns-width=10mm}@
-% $\begin{pNiceMatrix}
-% a & b \\ c & d \\
-% \end{pNiceMatrix}
-% = 
-% \begin{pNiceMatrix}
-% 1   & 1245 \\ 345 & 2 \\
-% \end{pNiceMatrix}$
-% \end{BVerbatim}
-% \begin{scope}
-% \NiceMatrixOptions{columns-width=10mm}
-% $\begin{pNiceMatrix}
-% a & b \\
-% c & d \\
-% \end{pNiceMatrix}
-% = 
-% \begin{pNiceMatrix}
-% 1   & 1245 \\
-% 345 & 2 \\
-% \end{pNiceMatrix}$
-% \end{scope}
-% 
-% 
-% \bigskip
-% But it's also possible to fix a zone where all the matrices will have their columns of the same width, equal to
-% the widest cell of all the matrices. This construction uses the environment |{NiceMatrixBlock}| with the option
-% |auto-columns-width|.\footnote{At this time, this is the only usage of the environment |{NiceMatrixBlock}| but
-% it may have other usages in the future.}
-%
-% \medskip
-% \begin{BVerbatim}[baseline=c,boxwidth=8.5cm]
-% ~emphase#\begin{NiceMatrixBlock}[auto-columns-width]@
-% $\begin{pNiceMatrix}
-% a & b \\ c & d \\
-% \end{pNiceMatrix}
-% = 
-% \begin{pNiceMatrix}
-% 1   & 1245 \\ 345 & 2 \\
-% \end{pNiceMatrix}$
-% ~emphase#\end{NiceMatrixBlock}@
-% \end{BVerbatim}
-% \begin{NiceMatrixBlock}[auto-columns-width]
-% $\begin{pNiceMatrix}
-% a & b \\ c & d \\
-% \end{pNiceMatrix}
-% = 
-% \begin{pNiceMatrix}
-% 1   & 1245 \\  345 & 2 \\
-% \end{pNiceMatrix}$
-% \end{NiceMatrixBlock}
-%
 % 
 % \section{The Tikz nodes created by nicematrix}
 % 
@@ -663,10 +565,157 @@ version 2005/12/01 or later.
 % \tikz[remember picture,overlay] 
 %      \draw (mymatrix-2-2) circle (2mm) ; 
 %
-%
 % \medskip
 % Don't forget the options |remember picture| and |overlay|.
 %
+% \bigskip
+% In the following example, we have underlined all the nodes of the matrix.
+% \begin{scope}
+% \tikzset{every node/.style = {fill = red!15, inner sep = 0pt}}
+% \[\begin{pNiceMatrix}
+% a & a + b & a + b + c \\
+% a & a     & a + b  \\
+% a & a     & a 
+% \end{pNiceMatrix}\]
+% \end{scope}
+% 
+%
+% \bigskip
+% In fact, the package \pkg{nicematrix} can create ``extra nodes''. These new nodes are created if the option
+% |create-extra-nodes| is used. There are two series of extra nodes: the ``medium nodes'' and the ``large nodes''.
+%
+% \medskip
+% The names of the ``medium nodes'' are constructed by adding the suffix ``|-medium|'' to the names of the ``normal
+% nodes''. In the following example, we have underlined the ``medium nodes''. We consider that this example is self-explanatory.
+% \[\begin{pNiceMatrix}
+% [create-extra-nodes,
+%  code-after = {\begin{tikzpicture}%
+%                   [every node/.style = {fill = red!15,
+%                                         blend mode = multiply,
+%                                         inner sep = -\pgflinewidth/2},
+%                    name suffix = -medium]
+%                \node [fit = (1-1)] {} ;
+%                \node [fit = (1-2)] {} ;
+%                \node [fit = (1-3)] {} ;
+%                \node [fit = (2-1)] {} ;
+%                \node [fit = (2-2)] {} ;
+%                \node [fit = (2-3)] {} ;
+%                \node [fit = (3-1)] {} ;
+%                \node [fit = (3-2)] {} ;
+%                \node [fit = (3-3)] {} ;
+%                \end{tikzpicture}}]
+% a & a + b & a + b + c \\
+% a & a     & a + b  \\
+% a & a     & a 
+% \end{pNiceMatrix}\]
+% 
+%
+% \medskip
+% The names of the ``large nodes'' are constructed by adding the suffix ``|-large|'' to the names of the ``normal
+% nodes''. In the following example, we have underlined the ``large nodes''. We consider that this example is
+% self-explanatory.\footnote{In the environments like |{pNiceArrayC}| and |{pNiceArrayRC}|, there is not ``large
+% nodes'' created in the exterior row and column.}
+%
+% \[\begin{pNiceMatrix}
+% [create-extra-nodes,
+%  code-after = {\begin{tikzpicture}%
+%                   [every node/.style = {blend mode = multiply,
+%                                         inner sep = -\pgflinewidth/2},
+%                    name suffix = -large]
+%                \node [fit = (1-1),fill = red!15] {} ;
+%                \node [fit = (1-3),fill = red!15] {} ;
+%                \node [fit = (2-2),fill = red!15] {} ;
+%                \node [fit = (3-1),fill = red!15] {} ;
+%                \node [fit = (3-3),fill = red!15] {} ;
+%                \node [fit = (1-2),fill = blue!15] {} ;
+%                \node [fit = (2-1),fill = blue!15] {} ;
+%                \node [fit = (2-3),fill = blue!15] {} ;
+%                \node [fit = (3-2),fill = blue!15] {} ;
+%                \end{tikzpicture}}]
+% a & a + b & a + b + c \\
+% a & a     & a + b  \\
+% a & a     & a 
+% \end{pNiceMatrix}\]
+% 
+%
+% \medskip
+% The ``large nodes'' of the first column and last column may appear too small for some usage. That's why it's
+% possible to use the options |left-margin| and |right-margin| to add space on both sides of the array and also
+% space in the ``large nodes'' of the first column and last column. In the following example, we have used the
+% options |left-margin| and |right-margin|.\footnote{The options |left-margin| and |right-margin| take dimensions
+% as values but, if no value is given, the default value is used, which is |\arraycolsep|.}
+% \[\begin{pNiceMatrix}
+% [create-extra-nodes,left-margin,right-margin,
+%  code-after = {\begin{tikzpicture}%
+%                   [every node/.style = {blend mode = multiply,
+%                                         inner sep = -\pgflinewidth/2},
+%                    name suffix = -large]
+%                \node [fit = (1-1),fill = red!15] {} ;
+%                \node [fit = (1-3),fill = red!15] {} ;
+%                \node [fit = (2-2),fill = red!15] {} ;
+%                \node [fit = (3-1),fill = red!15] {} ;
+%                \node [fit = (3-3),fill = red!15] {} ;
+%                \node [fit = (1-2),fill = blue!15] {} ;
+%                \node [fit = (2-1),fill = blue!15] {} ;
+%                \node [fit = (2-3),fill = blue!15] {} ;
+%                \node [fit = (3-2),fill = blue!15] {} ;
+%                \end{tikzpicture}}]
+% a & a + b & a + b + c \\
+% a & a     & a + b  \\
+% a & a     & a 
+% \end{pNiceMatrix}\]
+% 
+% \medskip
+% It's also possible to add more space on both side of the array with the options |extra-left-margin| and
+% |extra-right-margin|. These margins are not incorporated in the ``large nodes''. In the following example, we
+% have used |extra-left-margin| and |extra-right-margin| with the value $3$~pt.
+% \[\begin{pNiceMatrix}
+% [create-extra-nodes,left-margin,right-margin,extra-right-margin=3pt,extra-left-margin=3pt,
+%  code-after = {\begin{tikzpicture}%
+%                   [every node/.style = {blend mode = multiply,
+%                                         inner sep = -\pgflinewidth/2},
+%                    name suffix = -large]
+%                \node [fit = (1-1),fill = red!15] {} ;
+%                \node [fit = (1-3),fill = red!15] {} ;
+%                \node [fit = (2-2),fill = red!15] {} ;
+%                \node [fit = (3-1),fill = red!15] {} ;
+%                \node [fit = (3-3),fill = red!15] {} ;
+%                \node [fit = (1-2),fill = blue!15] {} ;
+%                \node [fit = (2-1),fill = blue!15] {} ;
+%                \node [fit = (2-3),fill = blue!15] {} ;
+%                \node [fit = (3-2),fill = blue!15] {} ;
+%                \end{tikzpicture}}]
+% a & a + b & a + b + c \\
+% a & a     & a + b  \\
+% a & a     & a 
+% \end{pNiceMatrix}\]
+%
+% \medskip
+% In this case, if we want a control over the height of the rows, we can add a |\strut| in each row of the array.
+% \[\begin{pNiceMatrix}
+% [create-extra-nodes,left-margin,right-margin,extra-right-margin=3pt,extra-left-margin=3pt,
+%  code-after = {\begin{tikzpicture}%
+%                   [every node/.style = {blend mode = multiply,
+%                                         inner sep = -\pgflinewidth/2},
+%                    name suffix = -large]
+%                \node [fit = (1-1),fill = red!15] {} ;
+%                \node [fit = (1-3),fill = red!15] {} ;
+%                \node [fit = (2-2),fill = red!15] {} ;
+%                \node [fit = (3-1),fill = red!15] {} ;
+%                \node [fit = (3-3),fill = red!15] {} ;
+%                \node [fit = (1-2),fill = blue!15] {} ;
+%                \node [fit = (2-1),fill = blue!15] {} ;
+%                \node [fit = (2-3),fill = blue!15] {} ;
+%                \node [fit = (3-2),fill = blue!15] {} ;
+%                \end{tikzpicture}}]
+% \strut a & a + b & a + b + c \\
+% \strut a & a     & a + b  \\
+% \strut a & a     & a 
+% \end{pNiceMatrix}\]
+%
+% \bigskip
+% We explain below how to fill the nodes created by \pkg{nicematrix}.
+%
 % \section{The code-after}
 %
 % The option |code-after| may be used to give some code that will be excuted after the construction of the matrix
@@ -675,7 +724,7 @@ version 2005/12/01 or later.
 % In the |code-after|, the Tikz nodes should be accessed by a name of the form $i$-$j$ (without the prefix of the
 % name of the environment).
 %
-% Morevover, a special command, called |\line| is available to draw directly dotted lines between nodes.
+% Moreover, a special command, called |\line| is available to draw directly dotted lines between nodes.
 %
 % \medskip
 % \begin{BVerbatim}[baseline=c,boxwidth=12cm]
@@ -700,7 +749,8 @@ version 2005/12/01 or later.
 % |L|, |C| and~|R|\footnote{The column types |L|, |C| and |R| are defined locally inside |{NiceArray}| with
 % |\newcolumntype| of \pkg{array}. This definition overrides an eventual previous definition.} instead of |l|, |c|
 % and |r|. It's possible to use the constructions \verb|w{...}{...}|, \verb|W{...}{...}|, \verb+|+, |>{...}|,
-% |<{...}|, |@{...}|, |!{...}| and |*{n}{...}| but the letters |p|, |m| and |b| should not be used.
+% |<{...}|, |@{...}|, |!{...}| and |*{n}{...}| but the letters |p|, |m| and |b| should not be used.\footnote{In a
+% command |\multicolumn|, one should also use the letters |L|, |C|, |R|.}
 %
 % \medskip
 % The environment |{NiceArray}| accepts the classical options |t|, |c| and |b| of |{array}| but also other options
@@ -755,7 +805,7 @@ version 2005/12/01 or later.
 %
 % The environment |{pNiceArrayC}| takes a mandatory argument which is the preamble of the array. The types
 % of columns available are the same as for the environment |{NiceArray}|. \textbf{However, no specification must be
-% given for the last column.} It will automatically (and necessarily) be a column~|L| column. 
+% given for the last column.} It will automatically (and necessarily) be a |L|~column. 
 % 
 % A special option, called |code-for-last-col|, specifies tokens that will be inserted before each cell of the last
 % column. The option |columns-width| doesn't apply to this external column.
@@ -785,7 +835,7 @@ version 2005/12/01 or later.
 %
 % \bigskip
 % In fact, the environment |{pNiceArrayC}| and its variants are based upon an more general environment, called
-% |{NiceArrayCwithDelims}|. The first two mandatory arguments of this environment are the left and right delimiter
+% |{NiceArrayCwithDelims}|. The first two mandatory arguments of this environment are the left and right delimiters
 % used in the construction of the matrix. It's possible to use |{NiceArrayCwithDelims}| if we want to use atypical
 % delimiters.
 %
@@ -815,10 +865,6 @@ version 2005/12/01 or later.
 % environment |{pNiceArrayC}|, no specification must be given for the last column (it will automatically be a |L|
 % column). 
 %
-% For technical reasons, the key |columns-width| is mandatory, with an numerical value (e.g. 1~cm) or with
-% the special value |auto|. This implies that all the columns of an environment |{pNiceArrayRC}| have necessarily
-% the same width.
-%
 % A special option, called |code-for-first-row|, specifies tokens that will be inserted before each cell of the
 % first row.
 %
@@ -826,8 +872,8 @@ version 2005/12/01 or later.
 % \begin{BVerbatim}[baseline=c,boxwidth=11cm]
 % $\begin{pNiceArrayRC}{CCC}%
 %   [columns-width = auto,
-%    code-for-first-row = {\color{blue}},
-%    code-for-last-col  = {\color{blue}}]
+%    code-for-first-row = \color{blue},
+%    code-for-last-col  = \color{blue}]
 % C_1 & C_2 & C_3 \\
 % 1 & 2 & 3 & L_1\\
 % 4 & 5 & 6 & L_2\\
@@ -835,27 +881,25 @@ version 2005/12/01 or later.
 % \end{pNiceArrayRC}$
 % \end{BVerbatim}
 % $\begin{pNiceArrayRC}{CCC}[columns-width=auto,
-%                            code-for-first-row = {\color{blue}},
-%                            code-for-last-col  = {\color{blue}}]
+%                            code-for-first-row = \color{blue},
+%                            code-for-last-col  = \color{blue}]
 % C_1 & C_2 & C_3 \\
 % 1 & 2 & 3 & L_1 \\
 % 4 & 5 & 6 & L_2 \\
 % 7 & 8 & 9 & L_3 \\
 % \end{pNiceArrayRC}$
 %
-% 
-% \bigskip
-% For technical reasons, the first line of the array (which will be composed ``above'' the main matrix)
-% must \emph{not} contain the command |\\| and no verbatim material.
 %
 % \bigskip
 % The first row of an environment |{pNiceArrayRC}| has the number $0$, and not $1$. This number is used for the
 % names of the Tikz nodes (the names of these nodes are used, for example, by the command |\line| in |code-after|).
 %
+% For technical reasons, it's not possible to use the option of the command |\\| after the first row (the placement
+% of the delimiters would be wrong).
 %
 % \bigskip
 % In fact, the environment |{pNiceArrayRC}| and its variants are based upon an more general environment, called
-% |{NiceArrayRCwithDelims}|. The first two mandatory arguments of this environment are the left and right delimiter
+% |{NiceArrayRCwithDelims}|. The first two mandatory arguments of this environment are the left and right delimiters
 % used in the construction of the matrix. It's possible to use |{NiceArrayRCwithDelims}| if we want to use atypical
 % delimiters.
 %
@@ -877,91 +921,267 @@ version 2005/12/01 or later.
 % 7 & 8 & 9 
 % \end{NiceArrayRCwithDelims}$
 %
-% 
-% 
-% \section{Technical remarks}
-%
-% \subsection{Diagonal lines} 
 %
-% By default, all the diagonal lines\footnote{We speak of the lines created by |\Ddots| and not the lines created
-% by a command |\line| in |code-after|.} of a same array are ``parallelized''. That means that the first diagonal
-% line is drawn and, then, the other lines are drawn parallel to the first one (by rotation around the left-most
-% extremity of the line). That's why the position of the instructions |\Ddots| in the array can have a marked
-% effect on the final result.
+% \bigskip
+% If we want to write a linear system, we can use the following code, with a preamble \verb+CCC|C+:
 %
-% \medskip
-% In the following examples, the first |\Ddots| instruction is written in color:
+% \medskip 
+% \begin{BVerbatim}[baseline=c,boxwidth=11cm]
+% $\begin{pNiceArrayRC}{~emphase#CCC|C@}
+% C_1 & \Cdots & C_n \\
+% a_{11} & \Cdots & a_{1n} & b_1 \\
+% \Vdots &      & \Vdots & \Vdots \\
+% a_{n1} & \Cdots & a_{nn} & b_n \\
+% \end{pNiceArrayRC}$
+% \end{BVerbatim}
+% $\begin{pNiceArrayRC}{CCC|C}
+% C_1 & \Cdots & C_n \\
+% a_{11} & \Cdots & a_{1n} & b_1 \\
+% \Vdots &      & \Vdots & \Vdots \\
+% a_{n1} & \Cdots & a_{nn} & b_n \\
+% \end{pNiceArrayRC}$
 % 
 % \medskip
-% \begin{scope}
-% \begin{minipage}{9.5cm}
-% Example with parallelization (default):
-% \begin{Verbatim}
-% $A = \begin{pNiceMatrix}
-% 1      & \Cdots &        & 1      \\
-% a+b    & ~emphase#\Ddots@~ &        & \Vdots \\
-% \Vdots & \Ddots &        &        \\
-% a+b    & \Cdots & a+b    & 1
-% \end{pNiceMatrix}$
-% \end{Verbatim}
-% \end{minipage}
-% $A = \begin{pNiceMatrix}
-% 1      & \Cdots &     & 1      \\
-% a+b    & \Ddots &     & \Vdots \\
-% \Vdots & \Ddots &     &        \\
-% a+b    & \Cdots & a+b & 1
-% \end{pNiceMatrix}$
+% The resultat may seem disappointing. It's possible to suppress the vertical rule in the first row with the
+% command |\multicolumn| in order to ``reconstruct'' the cell.
 % 
+%
 % \bigskip
-% \NiceMatrixOptions{parallelize-diags=true}%
-% \begin{minipage}{9.5cm}
-% % \begin{Verbatim}
-% $A = \begin{pNiceMatrix}
-% 1      & \Cdots &        & 1      \\
-% a+b    &        &        & \Vdots \\
-% \Vdots & ~emphase#\Ddots@~ & \Ddots &        \\
-% a+b    & \Cdots & a+b    & 1
-% \end{pNiceMatrix}$
-% \end{Verbatim}
-% \end{minipage}
-% $A = \begin{pNiceMatrix}
-% 1      & \Cdots &        & 1      \\
-% a+b    &        &        & \Vdots \\
-% \Vdots & \Ddots & \Ddots &        \\
-% a+b    & \Cdots & a+b    & 1
-% \end{pNiceMatrix}$
+% \begin{BVerbatim}[baseline=c,boxwidth=11cm]
+% $\begin{pNiceArrayRC}{CCC|C}
+% C_1 & \Cdots & ~emphase#\multicolumn{1}{C}{C_n}@ \\
+% a_{11} & \Cdots & a_{1n} & b_1 \\
+% \Vdots &      & \Vdots & \Vdots \\
+% a_{n1} & \Cdots & a_{nn} & b_n \\
+% \end{pNiceArrayRC}$
+% \end{BVerbatim}
+% $\begin{pNiceArrayRC}{CCC|C}
+% C_1 & \Cdots & \multicolumn{1}{C}{C_n} \\
+% a_{11} & \Cdots & a_{1n} & b_1 \\
+% \Vdots &      & \Vdots & \Vdots \\
+% a_{n1} & \Cdots & a_{nn} & b_n 
+% \end{pNiceArrayRC}$
 %
 % \bigskip
-% It's possible to turn off the parallelization with the option |parallelize-diags| set to |false|: \par\nobreak 
+% On the other side, we may remark that an horizontal line (with |\hline| or |\hdashline| of \pkg{arydshln})
+% doesn't extend in the ``exterior column'' of an environment like |{pNiceArrayC}| or |{pNiceArrayRC}|.
 %
 % \medskip
-% \NiceMatrixOptions{parallelize-diags=false}%
-% \begin{minipage}{9.5cm}
-% The same example without parallelization:
-% \end{minipage}
-% $A = \begin{pNiceMatrix}
-% 1      & \Cdots  &     & 1      \\
-% a+b    & \Ddots  &     & \Vdots \\
-% \Vdots & \Ddots  &     &        \\
-% a+b    & \Cdots  & a+b & 1
-% \end{pNiceMatrix}$
-%
-%
-% \end{scope}
-%
-% \subsection{The ``empty'' cells}
+% \begin{BVerbatim}[baseline=c,boxwidth=11cm]
+% $\begin{pNiceArrayC}{CCC}
+% a_{11} & \Cdots & a_{1n} & L_1 \\
+% \Vdots &        & \Vdots & \Vdots \\
+% a_{n1} & \Cdots & a_{nn} & L_n \\
+% ~emphase#\hdashline@
+% S_1    & \Cdots  & S_n \\
+% \end{pNiceArrayC}$
+% \end{BVerbatim}
+% $\begin{pNiceArrayC}{CCC}
+% a_{11} & \Cdots & a_{1n} & L_1 \\
+% \Vdots &        & \Vdots & \Vdots \\
+% a_{n1} & \Cdots & a_{nn} & L_n \\
+% \hdashline
+% S_1    & \Cdots  & S_n \\
+% \end{pNiceArrayC}$
 % 
-% An instruction like |\Ldots|, |\Cdots|, etc. tries to determine the first non-empty cell on both
-% sides\footnote{If \pkg{nicematrix} can't find these cells, an error |Imposible instruction| is raised. Nevertheless,
-% with the option |silent|, these instructions are discarded silently.}. However, a empty cell is not necessarily a
-% cell with no TeX content (that is to say a cell with no token between the two ampersands~|&|). Indeed, a cell
-% with contents |\hspace*{1cm}| may be considered as empty.
-%
-% \interitem
-% For \pkg{nicematrix}, the precise rules are as follow.
 %
-% \begin{itemize}
-% \item An implicit cell is empty. For example, in the following matrix:
+% \section{The width of the columns}
+% \label{width}
+%
+% In the environments with an explicit preamble (like |{NiceArray}|, |{pNiceArrayC}|, |{pNiceArrayRC}|, etc.), it's
+% possible to fix the  width of a given column with the standard letters |w| and |W| of the package \pkg{array}.
+% 
+% \medskip
+% \begin{BVerbatim}[baseline=c,boxwidth=10cm]
+% $\left(\begin{NiceArray}{~emphase#wc{1cm}@CC}
+% 1  & 12 & -123 \\
+% 12 & 0  & 0    \\
+% 4  & 1  & 2 
+% \end{NiceArray}\right)$
+% \end{BVerbatim}
+% $\left(\begin{NiceArray}{wc{1cm}CC}
+% 1  & 12 & -123 \\
+% 12 & 0  & 0    \\
+% 4  & 1  & 2 
+% \end{NiceArray}\right)$
+%
+%
+% \bigskip
+% It's also possible to fix the width of all the columns of a matrix directly with the option |columns-width| (in
+% all the environments of \pkg{nicematrix}).
+% 
+% \medskip
+% \begin{BVerbatim}[baseline=c,boxwidth=10cm]
+% $\begin{pNiceMatrix}[~emphase#columns-width = 1cm@]
+% 1  & 12 & -123 \\
+% 12 & 0  & 0    \\
+% 4  & 1  & 2 
+% \end{pNiceMatrix}$
+% \end{BVerbatim}
+% $\begin{pNiceMatrix}[columns-width = 1cm]
+% 1  & 12 & -123 \\
+% 12 & 0  & 0    \\
+% 4  & 1  & 2 
+% \end{pNiceMatrix}$
+%
+% \medskip
+% Note that the space inserted between two columns (equal to 2 |\arraycolsep|) is not suppressed.
+%
+% \bigskip
+% It's possible to give the value |auto| to the option |columns-width|: all the columns of the array will
+% have a width equal to the widest cell of the array. \textbf{Two or three compilations may be necessary.}\par\nobreak
+% \medskip
+% \begin{BVerbatim}[baseline=c,boxwidth=10cm]
+% $\begin{pNiceMatrix}[~emphase#columns-width = auto@]
+% 1  & 12 & -123 \\
+% 12 & 0  & 0    \\
+% 4  & 1  & 2 
+% \end{pNiceMatrix}$
+% \end{BVerbatim}
+% $\begin{pNiceMatrix}[columns-width = auto]
+% 1  & 12 & -123 \\
+% 12 & 0  & 0    \\
+% 4  & 1  & 2 
+% \end{pNiceMatrix}$
+% 
+% \bigskip
+% It's possible to fix the width of the columns of all the matrices of a current scope with the command
+% |\NiceMatrixOptions|.\par\nobreak 
+% \medskip
+% \begin{BVerbatim}[baseline=c,boxwidth=8.5cm]
+% ~emphase#\NiceMatrixOptions{columns-width=10mm}@
+% $\begin{pNiceMatrix}
+% a & b \\ c & d \\
+% \end{pNiceMatrix}
+% = 
+% \begin{pNiceMatrix}
+% 1   & 1245 \\ 345 & 2 \\
+% \end{pNiceMatrix}$
+% \end{BVerbatim}
+% \begin{scope}
+% \NiceMatrixOptions{columns-width=10mm}
+% $\begin{pNiceMatrix}
+% a & b \\
+% c & d \\
+% \end{pNiceMatrix}
+% = 
+% \begin{pNiceMatrix}
+% 1   & 1245 \\
+% 345 & 2 \\
+% \end{pNiceMatrix}$
+% \end{scope}
+% 
+% 
+% \bigskip
+% But it's also possible to fix a zone where all the matrices will have their columns of the same width, equal to
+% the widest cell of all the matrices. This construction uses the environment |{NiceMatrixBlock}| with the option
+% |auto-columns-width|.\footnote{At this time, this is the only usage of the environment |{NiceMatrixBlock}| but
+% it may have other usages in the future.}
+%
+% \medskip
+% \begin{BVerbatim}[baseline=c,boxwidth=8.5cm]
+% ~emphase#\begin{NiceMatrixBlock}[auto-columns-width]@
+% $\begin{pNiceMatrix}
+% a & b \\ c & d \\
+% \end{pNiceMatrix}
+% = 
+% \begin{pNiceMatrix}
+% 1   & 1245 \\ 345 & 2 \\
+% \end{pNiceMatrix}$
+% ~emphase#\end{NiceMatrixBlock}@
+% \end{BVerbatim}
+% \begin{NiceMatrixBlock}[auto-columns-width]
+% $\begin{pNiceMatrix}
+% a & b \\ c & d \\
+% \end{pNiceMatrix}
+% = 
+% \begin{pNiceMatrix}
+% 1   & 1245 \\  345 & 2 \\
+% \end{pNiceMatrix}$
+% \end{NiceMatrixBlock}
+%
+%
+% \section{Technical remarks}
+%
+% \subsection{Diagonal lines} 
+%
+% By default, all the diagonal lines\footnote{We speak of the lines created by |\Ddots| and not the lines created
+% by a command |\line| in |code-after|.} of a same array are ``parallelized''. That means that the first diagonal
+% line is drawn and, then, the other lines are drawn parallel to the first one (by rotation around the left-most
+% extremity of the line). That's why the position of the instructions |\Ddots| in the array can have a marked
+% effect on the final result.
+%
+% \medskip
+% In the following examples, the first |\Ddots| instruction is written in color:
+% 
+% \medskip
+% \begin{scope}
+% \begin{minipage}{9.5cm}
+% Example with parallelization (default):
+% \begin{Verbatim}
+% $A = \begin{pNiceMatrix}
+% 1      & \Cdots &        & 1      \\
+% a+b    & ~emphase#\Ddots@~ &        & \Vdots \\
+% \Vdots & \Ddots &        &        \\
+% a+b    & \Cdots & a+b    & 1
+% \end{pNiceMatrix}$
+% \end{Verbatim}
+% \end{minipage}
+% $A = \begin{pNiceMatrix}
+% 1      & \Cdots &     & 1      \\
+% a+b    & \Ddots &     & \Vdots \\
+% \Vdots & \Ddots &     &        \\
+% a+b    & \Cdots & a+b & 1
+% \end{pNiceMatrix}$
+% 
+% \bigskip
+% \NiceMatrixOptions{parallelize-diags=true}%
+% \begin{minipage}{9.5cm}
+% % \begin{Verbatim}
+% $A = \begin{pNiceMatrix}
+% 1      & \Cdots &        & 1      \\
+% a+b    &        &        & \Vdots \\
+% \Vdots & ~emphase#\Ddots@~ & \Ddots &        \\
+% a+b    & \Cdots & a+b    & 1
+% \end{pNiceMatrix}$
+% \end{Verbatim}
+% \end{minipage}
+% $A = \begin{pNiceMatrix}
+% 1      & \Cdots &        & 1      \\
+% a+b    &        &        & \Vdots \\
+% \Vdots & \Ddots & \Ddots &        \\
+% a+b    & \Cdots & a+b    & 1
+% \end{pNiceMatrix}$
+%
+% \bigskip
+% It's possible to turn off the parallelization with the option |parallelize-diags| set to |false|: \par\nobreak 
+%
+% \medskip
+% \NiceMatrixOptions{parallelize-diags=false}%
+% \begin{minipage}{9.5cm}
+% The same example without parallelization:
+% \end{minipage}
+% $A = \begin{pNiceMatrix}
+% 1      & \Cdots  &     & 1      \\
+% a+b    & \Ddots  &     & \Vdots \\
+% \Vdots & \Ddots  &     &        \\
+% a+b    & \Cdots  & a+b & 1
+% \end{pNiceMatrix}$
+%
+%
+% \end{scope}
+%
+% \subsection{The ``empty'' cells}
+% 
+% An instruction like |\Ldots|, |\Cdots|, etc. tries to determine the first non-empty cells on both sides. However,
+% a empty cell is not necessarily a cell with no TeX content (that is to say a cell with no token between the two
+% ampersands~|&|). Indeed, a cell with contents |\hspace*{1cm}| may be considered as empty.
+%
+% \interitem
+% For \pkg{nicematrix}, the precise rules are as follow.
+%
+% \begin{itemize}
+% \item An implicit cell is empty. For example, in the following matrix:
 %
 % \begin{Verbatim}
 % \begin{pmatrix}
@@ -977,7 +1197,7 @@ version 2005/12/01 or later.
 %
 % \medskip
 % \item A cell which contains a command |\Ldots|, |\Cdots|, |\Vdots|, |\Ddots| or |\Iddots| and their starred
-% versions is empty. We recall that theses commands should be used alone in a cell.
+% versions is empty. We recall that these commands should be used alone in a cell.
 %
 % \medskip
 % \item A cell with a command |\Hspace| (or |\Hspace*|) is empty. This command |\Hspace| is a command defined by
@@ -986,9 +1206,6 @@ version 2005/12/01 or later.
 % with \pkg{nicematrix}.
 % % \end{itemize}
 %
-% \interitem
-% A dotted line must be delimited by two non-empty cells. If it's not possible to find one of these cells whitin
-% the boundaries of the matrix, an error is issued and the instruction is ignored.
 %
 % \subsection{The option exterior-arraycolsep}
 % 
@@ -999,17 +1216,96 @@ version 2005/12/01 or later.
 % (perhaps we should instead remove it from array in general, but that's a harder task).} It's possible to suppress
 % these spaces for a given environment |{array}| with a construction like |\begin{array}{@{}ccccc@{}}|.}
 %
-% The environment |{matrix}| and its variants (|{pmatrix}|, |{vmatrix}|, etc.) of \pkg{amsmath} and \pkg{mathtools}
-% prefer to delete these spaces with explicit instructions |\hskip -\arraycolsep| and |{NiceArray}| does likewise.
+% The environment |{matrix}| and its variants (|{pmatrix}|, |{vmatrix}|, etc.) of \pkg{amsmath} prefer to delete
+% these spaces with explicit instructions |\hskip -\arraycolsep| and |{NiceArray}| does likewise.
 %
-% However, the user can change this behaviour with the boolean option |exterior-arraycolsep|. With this option,
-% |{NiceArray}| will insert the same horizontal spaces as the environment |{array}|. This
-% option can be set for a given environment or globally with the command |\NiceMatrixOptions|. 
+% However, the user can change this behaviour with the boolean option |exterior-arraycolsep| of the command
+% |\NiceMatrixOptions|. With this option, |{NiceArray}| will insert the same horizontal spaces as the environment
+% |{array}|. 
 %
+% This option is also for ``compatibility'' since the package \pkg{nicematrix} provides a more precise control with
+% the options |left-margin|, |right-margin|, |extra-left-margin| and |extra-right-margin|.
+%
+%
+% \subsection{A technical problem with the argument of \textbackslash\textbackslash}
+%
+% For technical, reasons, if you use the optional argument of the command |\\|, the vertical space added will also
+% be added to the ``normal'' node corresponding at the previous node.
+%
+% \medskip
+% \begin{BVerbatim}[baseline=c,boxwidth=11cm]
+%      \begin{pNiceMatrix}
+%      a & \frac AB \\~emphase#[2mm]@
+%      b & c
+%      \end{pNiceMatrix}
+% \end{BVerbatim}
+% $\begin{pNiceMatrix}
+%   [code-after = {\tikz \node [inner sep = 0pt,
+%                               fill = red!15,
+%                               blend mode = multiply,
+%                               fit = (1-2) ] {} ; } ]
+% a & \frac AB \\[2mm]
+% b & c
+% \end{pNiceMatrix}$
+%
+% \bigskip
+% There are two solutions to solve this problem. The first solution is to use a TeX command to insert space between
+% the rows.
+%
+% \medskip
+% \begin{BVerbatim}[baseline=c,boxwidth=11cm]
+%      \begin{pNiceMatrix}
+%      a & \frac AB \\
+%      ~emphase#\noalign{\kern2mm}@
+%      b & c
+%      \end{pNiceMatrix}
+% \end{BVerbatim}
+% $\begin{pNiceMatrix}
+%   [code-after = {\tikz \node [inner sep = 0pt,
+%                               fill = red!15,
+%                               blend mode = multiply,
+%                               fit = (1-2) ] {} ; } ]
+% a & \frac AB \\
+% \noalign{\kern2mm}
+% b & c
+% \end{pNiceMatrix}$
 %
-% \section{Examples}
 %
 % \bigskip
+% The other solution is to use the command |\multicolumn| in the previous cell.
+%
+% \medskip
+% \begin{BVerbatim}[baseline=c,boxwidth=11cm]
+%      \begin{pNiceMatrix}
+%      a & ~emphase#\multicolumn1C{\frac AB}@ \\[2mm]
+%      b & c
+%      \end{pNiceMatrix}
+% \end{BVerbatim}
+% $\begin{pNiceMatrix}
+%   [code-after = {\tikz \node [inner sep = 0pt,
+%                               fill = red!15,
+%                               blend mode = multiply,
+%                               fit = (1-2) ] {} ; } ]
+% a & \multicolumn1C{\frac AB} \\[2mm]
+% b & c
+% \end{pNiceMatrix}$
+%
+%
+% \subsection{A remark concerning a bug of Tikz}
+%
+% Due to a bug in Tikz, the construction |-- cycle| in a Tikz path is incompatible with the use of |name prefix|
+% and |name suffix|.\footnote{cf. |tex.stackexchange.com/questions/327007/tikz-fill-not-being-drawn-using-named-coordinates|}
+%
+% \bigskip
+% Since |name prefix| is implicitly used in the |code-after| of \pkg{nicematrix}, it's not
+% possible to use |-- cycle| in |code-after|. 
+%
+%
+% \section{Examples}
+%
+% \subsection{Dotted lines}
+%
+% \medskip
 % A tridiagonal matrix:
 % 
 % \bigskip
@@ -1060,8 +1356,7 @@ version 2005/12/01 or later.
 %
 % \vspace{2cm}
 %
-% An example with |\Iddots|: 
-% 
+% An example with |\Iddots|: \par\nobreak
 % \bigskip
 % \begin{BVerbatim}[baseline=c]
 % $\begin{pNiceMatrix}
@@ -1079,29 +1374,72 @@ version 2005/12/01 or later.
 % 1       & 0       & \Cdots  & 0 
 % \end{pNiceMatrix}$
 %
-% \vspace{2cm}
 %
-% An example for the resultant of two polynoms :
+% \vspace{2cm}
+% An example with |\multicolumn|:\par\nobreak
+% \bigskip
+% \begin{BVerbatim}
+% \begin{pNiceMatrix}[nullify-dots]
+% 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10\\
+% 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10\\
+% \Cdots &  & ~emphase#\multicolumn{6}{C}{10 \text{ other rows}}@ & \Cdots \\
+% 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10
+% \end{pNiceMatrix}
+% \end{BVerbatim}
+% 
+% \bigskip
+% \[\begin{pNiceMatrix}[nullify-dots]
+% 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10\\
+% 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10\\
+% \Cdots &  & \multicolumn{6}{C}{10 \text{ other rows}} & \Cdots \\
+% 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10
+% \end{pNiceMatrix}\]
+% 
+% \vspace{2cm}
+% An example with |\Hdotsfor|:\par\nobreak
+% \bigskip
+% \begin{BVerbatim}[baseline=c,boxwidth=11cm]
+% \begin{pNiceMatrix}[nullify-dots]
+% 0 & 1 & 1 & 1 & 1 & 0 \\
+% 0 & 1 & 1 & 1 & 1 & 0 \\
+% \Vdots  & ~emphase#\Hdotsfor{4}@ & \Vdots \\
+%  & ~emphase#\Hdotsfor{4}@ & \\
+%  & ~emphase#\Hdotsfor{4}@ & \\
+%  & ~emphase#\Hdotsfor{4}@ & \\
+% 0 & 1 & 1 & 1 & 1 & 0 
+% \end{pNiceMatrix}
+% \end{BVerbatim}
+% $\begin{pNiceMatrix}[nullify-dots]
+% 0 & 1 & 1 & 1 & 1 & 0 \\
+% 0 & 1 & 1 & 1 & 1 & 0 \\
+% \Vdots  & \Hdotsfor{4} & \Vdots \\
+%  & \Hdotsfor{4} & \\
+%  & \Hdotsfor{4} & \\
+%  & \Hdotsfor{4} & \\
+% 0 & 1 & 1 & 1 & 1 & 0 
+% \end{pNiceMatrix}$
 %
+% \vspace{2cm}
+% An example for the resultant of two polynoms (the dashed line has been drawn with \pkg{arydshln}):\par\nobreak
 % \bigskip
 % \begin{BVerbatim}
 % \setlength{\extrarowheight}{1mm}
-% \[\begin{vNiceMatrix}[columns-width=6mm]
-% a_0    &       &&       &b_0    &       &     \\
-% a_1    &\Ddots &&       &b_1    &\Ddots &     \\
-% \Vdots &\Ddots &&       &\Vdots &\Ddots &b_0  \\
-% a_p    &       &&a_0    &       &       &b_1   \\
-%        &\Ddots &&a_1    &b_q    &       &\Vdots\\
-%        &       &&\Vdots &       &\Ddots &      \\
-%        &       &&a_p    &       &       &b_q    \\
-% \end{vNiceMatrix}\]
+% \[\begin{NiceArray}{|CCCC:CCC|}[columns-width=6mm]
+% a_0   &      &&       &b_0    &      &     \\
+% a_1   &\Ddots&&       &b_1    &\Ddots&     \\
+% \Vdots&\Ddots&&       &\Vdots &\Ddots&b_0  \\
+% a_p   &      &&a_0    &       &      &b_1   \\
+%       &\Ddots&&a_1    &b_q    &      &\Vdots\\
+%       &      &&\Vdots &       &\Ddots&      \\
+%       &      &&a_p     &       &      &b_q    \\
+% \end{NiceArray}\]
 % \end{BVerbatim}
 % 
 % \bigskip
 %
 % \begin{scope}
 % \setlength{\extrarowheight}{1mm}
-% \[\begin{vNiceMatrix}[columns-width=6mm]
+% \[\begin{NiceArray}{|CCCC:CCC|}[columns-width=6mm]
 % a_0   &      &&       &b_0    &      &     \\
 % a_1   &\Ddots&&       &b_1    &\Ddots&     \\
 % \Vdots&\Ddots&&       &\Vdots &\Ddots&b_0  \\
@@ -1109,12 +1447,14 @@ version 2005/12/01 or later.
 %       &\Ddots&&a_1    &b_q    &      &\Vdots\\
 %       &      &&\Vdots &       &\Ddots&      \\
 %       &      &&a_p     &       &      &b_q    \\
-% \end{vNiceMatrix}\]
+% \end{NiceArray}\]
 % \end{scope}   
 %
 %
-% \vspace{2cm}
-% In the following example, we use the environment |{NiceMatrixBlock}| with the option |auto-columns-width| because
+% \subsection{Width of the columns}
+%
+% \medskip
+% In the following example, we use |{NiceMatrixBlock}| with the option |auto-columns-width| because
 % we want the same automatic width for all the columns of the matrices.
 %
 % \bigskip
@@ -1193,32 +1533,104 @@ version 2005/12/01 or later.
 % \end{NiceMatrixBlock}
 % \end{multicols}
 % 
-% \vspace{2cm}
+% 
+% \subsection{How to highlight cells of the matrix}
+%
+% \medskip
+% In order to highlight a cell of a matrix, it's possible to ``draw'' one of the correspond nodes (the ``normal
+% node'', the ``medium node'' or the ``large node''). In the following example, we use the ``large nodes'' of the
+% diagonal of the matrix (with the Tikz key ``|name suffix|'', it's easy to use the ``large nodes''). In order to
+% have the continuity of the lines, we have to set |inner sep = -\pgflinewidth/2|.
+%
+% \begin{Verbatim}
+% $\left(\,\begin{NiceArray}{>{\strut}CCCC}
+%    [create-extra-nodes,left-margin,right-margin,
+%     code-after = {\begin{tikzpicture}
+%                      [~emphase#name suffix = -large@,
+%                       every node/.style = {draw,
+%                                            ~emphase#inner sep = -\pgflinewidth/2@}]
+%                      \node [fit = (1-1)] {} ; 
+%                      \node [fit = (2-2)] {} ; 
+%                      \node [fit = (3-3)] {} ; 
+%                      \node [fit = (4-4)] {} ; 
+%                   \end{tikzpicture}}]
+% a_{11} & a_{12} & a_{13} & a_{14} \\
+% a_{21} & a_{22} & a_{23} & a_{24} \\
+% a_{31} & a_{32} & a_{33} & a_{34} \\
+% a_{41} & a_{42} & a_{43} & a_{44} 
+% \end{NiceArray}\,\right)$
+% \end{Verbatim}
+%
 %
-% In the following example, we want to highlight a row of the matrix. To do so, we create a rectangular Tikz node
-% which encompasses the nodes of the second row with the Tikz library |fit|. This Tikz node is filled
-% after the construction of the matrix. In order to see the text \emph{under} this node, we have to use
-% transparency with the |blend mode| equal to |multiply|. 
+% \[\left(\,\begin{NiceArray}{>{\strut}CCCC}
+%    [create-extra-nodes,left-margin,right-margin,
+%     code-after = {\begin{tikzpicture}[name suffix = -large,
+%                                       every node/.style = {draw,
+%                                                            inner sep = -\pgflinewidth/2}]
+%                      \node [fit = (1-1)] {} ; 
+%                      \node [fit = (2-2)] {} ; 
+%                      \node [fit = (3-3)] {} ; 
+%                      \node [fit = (4-4)] {} ; 
+%                   \end{tikzpicture}}]
+% a_{11} & a_{12} & a_{13} & a_{14} \\
+% a_{21} & a_{22} & a_{23} & a_{24} \\
+% a_{31} & a_{32} & a_{33} & a_{34} \\
+% a_{41} & a_{42} & a_{43} & a_{44} 
+% \end{NiceArray}\,\right)\]
 % 
+%
+% \vspace{1cm}
+% The package \pkg{nicematrix} is constructed upon the environment |{array}| and, therefore, it's possible to use
+% the package \pkg{colortbl} in the environments of \pkg{nicematrix}.
+%
+% \medskip
+% \begin{BVerbatim}[baseline=c]
+% $\begin{bNiceMatrix}
+% 0 & \Cdots & 0 \\
+% ~emphase#\rowcolor{red!15}@ 1 & \Cdots & 1 \\
+% 0 & \Cdots & 0 \\
+% \end{bNiceMatrix}$
+% \end{BVerbatim}
+% \hspace{2cm}
+% $\begin{bNiceMatrix}
+% 0 & \Cdots & 0 \\
+% \rowcolor{red!15} 1 & \Cdots & 1 \\
+% 0 & \Cdots & 0 \\
+% \end{bNiceMatrix}$
+%
+% \medskip
+% The result may be disappointing. We therefore propose another method to highlight a row of the matrix. We
+% create a rectangular Tikz node which encompasses the nodes of the second row with the Tikz library \pkg{fit}. This
+% Tikz node is filled after the construction of the matrix. In order to see the text \emph{under} this node, we
+% have to use transparency with the |blend mode| equal to |multiply|. Warning: some \textsc{pdf} readers are not
+% able to render transparency correctly.
+%
+% \tikzset{highlight/.style={rectangle,
+%                            fill=red!15,
+%                            blend mode = multiply, 
+%                            rounded corners = 0.5 mm, 
+%                            inner sep=1pt}}
+%
 % \medskip
 % \begin{Verbatim}
 % \tikzset{highlight/.style={rectangle,
 %                            fill=red!15,
 %                            ~emphase#blend mode = multiply@,
+%                            rounded corners = 0.5 mm, 
 %                            inner sep=1pt}}
 %
-% $\begin{pNiceMatrix}[~emphase#code-after = {\tikz \node[highlight, fit = (2-1) (2-3)] {} ;}@]
+% $\begin{bNiceMatrix}[~emphase#code-after = {\tikz \node[highlight, fit = (2-1) (2-3)] {} ;}@]
 % 0 & \Cdots & 0 \\
 % 1 & \Cdots & 1 \\
 % 0 & \Cdots & 0 \\
-% \end{pNiceMatrix}$
+% \end{bNiceMatrix}$
 % \end{Verbatim}
 % 
-% \[\begin{pNiceMatrix}[code-after = {\tikz \node[highlight, fit = (2-1) (2-3)] {} ;}]
+% \[\begin{bNiceMatrix}[code-after = {\tikz \node[highlight, fit = (2-1) (2-3)] {} ;}]
 % 0 & \Cdots & 0 \\
 % 1 & \Cdots & 1 \\
 % 0 & \Cdots & 0 \\
-% \end{pNiceMatrix}\]
+% \end{bNiceMatrix}\]
 % 
 %
 % \bigskip
@@ -1226,7 +1638,7 @@ version 2005/12/01 or later.
 % following code, in the preamble, should activate blend modes in this way of compilation.
 %
 %
-%
+% \begin{scope} \small
 % |\ExplSyntaxOn|
 %
 % |\makeatletter|
@@ -1240,6 +1652,173 @@ version 2005/12/01 or later.
 % |\makeatother|
 %
 % |\ExplSyntaxOff|
+% \end{scope}
+% 
+% \vspace{1cm}
+% Considerer now the following matrix which we have named |example|.
+%
+% \medskip
+% \begin{Verbatim}
+% $\begin{pNiceArrayC}{CCC}[~emphase#name=example@,create-extra-nodes]
+% a & a + b & a + b + c & L_1\\
+% a & a     & a + b     & L_2 \\
+% a & a     & a         & L_3
+% \end{pNiceArrayC}$
+% \end{Verbatim}
+%                           
+% \[\begin{pNiceArrayC}{CCC}
+% a & a + b & a + b + c & L_1\\
+% a & a     & a + b     & L_2 \\
+% a & a     & a         & L_3
+% \end{pNiceArrayC}\]
+% 
+% \bigskip
+% If we want to highlight each row of this matrix, we can use the previous technique three times.
+%
+% \begin{Verbatim}
+% \tikzset{myoptions/.style={remember picture, 
+%                            overlay,
+%                            name prefix = example-,
+%                            every node/.style = {fill = red!15,
+%                                                 blend mode = multiply,
+%                                                 inner sep = 0pt}}}
+% \end{Verbatim}
+% 
+%
+% \tikzset{myoptions/.style={remember picture, 
+%                            overlay,
+%                            name prefix = example-,
+%                            every node/.style = {fill = red!15,
+%                                                 blend mode = multiply,
+%                                                 inner sep = 0pt}}}
+%
+% \begin{Verbatim}
+% \begin{tikzpicture}[myoptions]
+% \node [fit = (1-1) (1-3)] {} ;
+% \node [fit = (2-1) (2-3)] {} ;
+% \node [fit = (3-1) (3-3)] {} ;
+% \end{tikzpicture}
+% \end{Verbatim}
+%
+% \medskip
+% We obtain the following matrix.
+% 
+% \[\begin{pNiceArrayC}{CCC}
+%     [create-extra-nodes,
+%      code-after = {\begin{tikzpicture}[every node/.style = {fill = red!15,
+%                                                             blend mode = multiply,
+%                                                             inner sep = 0pt}]
+%                    \node [fit = (1-1) (1-3)] {} ;
+%                    \node [fit = (2-1) (2-3)] {} ;
+%                    \node [fit = (3-1) (3-3)] {} ;
+%                    \end{tikzpicture}}]
+% a & a + b & a + b + c & L_1\\
+% a & a     & a + b     & L_2 \\
+% a & a     & a         & L_3
+% \end{pNiceArrayC}\]
+%
+% \medskip
+% The result may seem disappointing. We can improve it by using the ``medium nodes'' instead of the ``normal nodes''.
+%
+% \begin{Verbatim}
+% \begin{tikzpicture}[myoptions, ~emphase#name suffix = -medium@]
+% \node [fit = (1-1) (1-3)] {} ;
+% \node [fit = (2-1) (2-3)] {} ;
+% \node [fit = (3-1) (3-3)] {} ;
+% \end{tikzpicture}
+% \end{Verbatim}
+%
+% \medskip
+% We obtain the following matrix.
+% 
+% \[\begin{pNiceArrayC}{CCC}
+%     [create-extra-nodes,
+%      code-after = {\begin{tikzpicture}[every node/.style = {fill = red!15,
+%                                                             blend mode = multiply,
+%                                                             inner sep = 0pt},
+%                                        name suffix = -medium]
+%                    \node [fit = (1-1) (1-3)] {} ;
+%                    \node [fit = (2-1) (2-3)] {} ;
+%                    \node [fit = (3-1) (3-3)] {} ;
+%                    \end{tikzpicture}}]
+% a & a + b & a + b + c & L_1\\
+% a & a     & a + b     & L_2 \\
+% a & a     & a         & L_3
+% \end{pNiceArrayC}\]
+%
+%                           
+% \vspace{1cm}
+% 
+% In the following example, we use the ``large nodes'' to highlight a zone of the matrix.\par\nobreak
+% \begin{Verbatim}
+% \left(\,\begin{NiceArray}{>{\strut}CCCC}
+%    [create-extra-nodes,left-margin,right-margin,
+%     code-after = {\tikz \path [~emphase#name suffix = -large@,
+%                                fill = red!15, 
+%                                blend mode = multiply]
+%                         (1-1.north west)
+%                      |- (2-2.north west)
+%                      |- (3-3.north west)
+%                      |- (4-4.north west)
+%                      |- (4-4.south east)
+%                      |- (1-1.north west) ; } ]
+% A_{11} & A_{12} & A_{13} & A_{14} \\
+% A_{21} & A_{22} & A_{23} & A_{24} \\
+% A_{31} & A_{32} & A_{33} & A_{34} \\
+% A_{41} & A_{42} & A_{43} & A_{44}  
+% \end{NiceArray}\,\right)
+% \end{Verbatim}
+%                              
+% \[\left(\,\begin{NiceArray}{>{\strut}CCCC}
+%    [create-extra-nodes,left-margin,right-margin,
+%     code-after = {\tikz \path [name suffix = -large,
+%                                fill = red!15, 
+%                                blend mode = multiply]
+%                         (1-1.north west)
+%                      |- (2-2.north west)
+%                      |- (3-3.north west)
+%                      |- (4-4.north west)
+%                      |- (4-4.south east)
+%                      |- (1-1.north west) ; } ]
+% A_{11} & A_{12} & A_{13} & A_{14} \\
+% A_{21} & A_{22} & A_{23} & A_{24} \\
+% A_{31} & A_{32} & A_{33} & A_{34} \\
+% A_{41} & A_{42} & A_{43} & A_{44}  
+% \end{NiceArray}\,\right)\]
+%
+% 
+% \subsection{Block matrices}
+%
+% \medskip
+% In the following example, we use the ``large nodes'' to construct a block matrix (the dashed lines have been
+% drawn with \pkg{arydshln}).
+% \begin{Verbatim}
+% \left(\begin{NiceArray}{CC:CC}
+%    [create-extra-nodes,
+%     ~emphase#code-after = { \tikz \node [fit = (1-1-large) (2-2-large), inner sep = 0 pt]@
+%     ~emphase#                           {$0_{22}$} ; }@ ]
+%        &        & a_{13} & a_{14} \\
+%        &        & a_{23} & a_{24} \\
+% \hdashline
+% a_{31} & a_{32} & a_{33} & a_{34} \\
+% a_{41} & a_{42} & a_{34} & a_{44} 
+% \end{NiceArray}\right)
+% \end{Verbatim}
+% 
+%                              
+% \[D = \left(\begin{NiceArray}{CC:CC}
+%    [create-extra-nodes,
+%     code-after = { \tikz \node [fit = (1-1-large) (2-2-large), inner sep = 0 pt] 
+%                                {$0_{22}$} ; } ]
+%        &        & a_{13} & a_{14} \\
+%        &        & a_{23} & a_{24} \\
+% \hdashline
+% a_{31} & a_{32} & a_{33} & a_{34} \\
+% a_{41} & a_{42} & a_{34} & a_{44} 
+% \end{NiceArray}\right)\]
+% 
+%
+% 
 % 
 % \section{Implementation}
 %
@@ -1248,8 +1827,7 @@ version 2005/12/01 or later.
 % \smallskip
 % However, when the option |renew-dots| is used, the commands |\cdots|, |\ldots|, |\dots|, |\vdots|, |\ddots| and
 % |\iddots| are redefined in the environments provided by \pkg{nicematrix} as explained previously. In the same way,
-% if the option |renew-matrix| is used, the environment |{matrix}| of \pkg{amsmath} (and \pkg{mathtools}) is
-% redefined.
+% if the option |renew-matrix| is used, the environment |{matrix}| of \pkg{amsmath} is redefined.
 %
 % \smallskip
 % On the other hand, the environment |{array}| is never redefined.
@@ -1264,6 +1842,16 @@ version 2005/12/01 or later.
 %
 % \subsection{Declaration of the package and extensions loaded}
 %
+% First, \pkg{tikz} and the Tikz library |fit| are loaded before the |\ProvidesExplPackage|.
+% They are loaded this way because |\usetifkzlibrary| in |expl3| code fails.\footnote{cf.
+% |tex.stackexchange.com/questions/57424/using-of-usetikzlibrary-in-an-expl3-package-fails|} 
+% 
+%
+%    \begin{macrocode}
+\RequirePackage{tikz}
+\usetikzlibrary{fit}
+%    \end{macrocode}
+% 
 % We give the traditionnal declaration of a package written with |expl3|:
 %    \begin{macrocode}
 \RequirePackage{l3keys2e}
@@ -1271,28 +1859,42 @@ version 2005/12/01 or later.
   {nicematrix}
   {\myfiledate}
   {\myfileversion}
-  {Draws nice dotted lines in matrix environments}
+  {Several features to improve the typesetting of mathematical matrices with TikZ}
 %    \end{macrocode}
 % 
 % The command for the treatment of the options of |\usepackage| is at the end of this package for technical reasons.
 %
 % \bigskip
-% We load \pkg{array}, \pkg{mathtools} (\pkg{mathtools} may be considered as the successor of \pkg{amsmath}) and \pkg{tikz}.
+% We load \pkg{array} and \pkg{amsmath}.
 %    \begin{macrocode}
 \RequirePackage{array}
-\RequirePackage{mathtools}
-\RequirePackage{tikz}
+\RequirePackage{amsmath}
 %    \end{macrocode}
 %
 % \bigskip 
 % The package \pkg{xparse} will be used to define the environment |{NiceMatrix}|, its variants and the
 % document-level commands (|\NiceMatrixOptions|, etc.).
-% \begin{macrocode}
+%    \begin{macrocode}
 \RequirePackage{xparse}
 %    \end{macrocode}
 %
 % \subsection{Technical  definitions}
+%
+%    \begin{macrocode}
+\cs_new_protected:Nn \@@_msg_error:n 
+        {\msg_error:nn {nicematrix} {#1}}
+\cs_new_protected:Nn \@@_msg_error:nn
+        {\msg_error:nn {nicematrix} {#1} {#2}}
+%    \end{macrocode}
 % 
+% \medskip
+%    \begin{macrocode}
+\cs_new_protected:Nn \@@_bool_new:N
+      {\bool_if_exist:NTF #1
+         {\bool_set_false:N #1}
+         {\bool_new:N #1}}
+%    \end{macrocode}
+%                              
 % First, we define a command |\iddots| similar to |\ddots| ($\ddots$) but with dots going forward ($\iddots$). We
 % use |\ProvideDocumentCommand| of \pkg{xparse}, and so, if the command |\iddots| has already been defined (for
 % example by the package \pkg{mathdots}), we don't define it again.
@@ -1311,17 +1913,6 @@ version 2005/12/01 or later.
 %
 % This definition is a variant of the standard definition of |\ddots|.
 %
-% \bigskip
-% In the environment |{NiceMatrix}|, the command |\multicolumn| will be linked to the following command
-% |\@@_multicolumn:nn| but only if the option |renew-matrix| is not set. Indeed, if the option |renew-matrix| is used,
-% we want to let the possibility to the user to use |\multicolumn| in some matrices without dotted lines and to
-% have the automatic dotted lines of \pkg{nicematrix} in other matrices. 
-%    \begin{macrocode}
-\cs_new_protected:Nn \@@_multicolumn:nn
-       {\msg_error:nn {nicematrix} {Multicolumn~forbidden}}
-%    \end{macrocode}
-% This command |\@@_multicolumn:nn| takes two arguments, and therefore, the first two arguments of |\column| will
-% be gobbled.
 %
 % \bigskip 
 % The following counter will count the environments |{NiceArray}|. The value of this counter will be used to
@@ -1339,47 +1930,40 @@ version 2005/12/01 or later.
 %
 % \bigskip
 % The sequence |\g_@@_names_seq| will be the list of all the names of environments used (via the option |name|) in
-% the document : two environments must not have the same name.
+% the document: two environments must not have the same name.
 %    \begin{macrocode}
 \seq_new:N \g_@@_names_seq
 %    \end{macrocode}
 %
 % \bigskip
-% The integer |\l_@@_number_of_first_row_int| is the number of the first row of the array. With a value of $0$ (the
-% default), the first row of the array will have the number~$1$. Within the environment |{NiceArrayRC}|, we will give
-% the value $-1$ to |\l_@@_number_of_first_row_int| and, therefore, the first row of the array will have the number~$0$.
+% The integer |\l_@@_nb_first_row_int| is the number of the first row of the array. The default value is $1$, but,
+% in the environments like |{pNiceArrayRC}|, the value will be~$0$.
 %    \begin{macrocode}
-\int_new:N \l_@@_number_of_first_row_int
+\int_new:N \l_@@_nb_first_row_int
+\int_set:Nn \l_@@_nb_first_row_int 1
 %    \end{macrocode}
 % 
 % \bigskip
-% The flag |\l_@@_direct_NiceArray_bool| will indicate if the current environment |{NiceArray}| is ``direct'' : that
-% means that it is not encompassed in another environment of the extension \pkg{nicematrix} like |{NiceMatrix}| or
-% |{pNiceArrayC}|. 
+% The flag |\l_@@_exterior_column_bool| will indicate if we are in an environment of the type of |{pNiceArrayC}| or
+% |{pNiceArrayRC}|. It will be used for the creation of the ``large nodes''.
 %    \begin{macrocode}
-\bool_new:N \l_@@_direct_NiceArray_bool
-\bool_set_true:N \l_@@_direct_NiceArray_bool
+\bool_new:N \l_@@_exterior_column_bool
 %    \end{macrocode}
 % 
-% \bigskip
-% The token list |\l_@@_code_for_cell_tl| is a code that will be inserted in the beginning of each cell of the
-% array (before the symbol |$| of the mathematical mode).
-%    \begin{macrocode}
-\tl_new:N \l_@@_code_for_cell_tl
-%    \end{macrocode}
-%
+% \bigskip 
 % \subsection{The options}
 %
 % The token list |\l_@@_pos_env_tl| will contain one of the three values |t|, |c| or |b| and will indicate the
-% position of the environment as in the option of the environment |{array}|. For the environment |{NiceMatrix}|
-% (and its variants) and |{pNiceArrayC}| (and its variants), the value will programmatically be fixed to |c|. For the
+% position of the environment as in the option of the environment |{array}|. For the environment |{pNiceMatrix}|,
+% |{pNiceArrayC}|,|{pNiceArrayRC}| and their variants, the value will programmatically be fixed to |c|. For the
 % environment |{NiceArray}|, however, the three values |t|, |c| and |b| are possible.
 %    \begin{macrocode}
 \tl_new:N \l_@@_pos_env_tl 
 \tl_set:Nn \l_@@_pos_env_tl c
 %    \end{macrocode}
 % 
-% The boolean |\l_@@_exterior_arraycolsep_bool| corresponds to the option |exterior-arraycolsep|. If this option is
+% \bigskip
+% The flag |\l_@@_exterior_arraycolsep_bool| corresponds to the option |exterior-arraycolsep|. If this option is
 % set, a space equal to |\arraycolsep| will be put on both sides of an environment |{NiceArray}| (but neither for
 % |{NiceMatrix}|, |{pNiceArrayC}|, |{pNiceArrayRC}| and their variants even if these environments rely upon |{NiceArray}|).
 %    \begin{macrocode}
@@ -1402,11 +1986,6 @@ version 2005/12/01 or later.
 \bool_new:N \l_@@_nullify_dots_bool
 %    \end{macrocode}
 %
-% \bigskip
-% The flag |\l_@@_renew_matrix_bool| will be raised if the option |renew-matrix| is used.
-%    \begin{macrocode}
-\bool_new:N \l_@@_renew_matrix_bool
-%    \end{macrocode}
 %
 % \bigskip
 % The following flag will be used when the current options specify that all the columns of the array must have the
@@ -1423,14 +2002,44 @@ version 2005/12/01 or later.
 \tl_new:N \l_@@_code_for_last_col_tl
 %    \end{macrocode}
 % 
-
 % \bigskip
-% The token list |\g_@@_name_tl| will contain the optional name of the environment : this name can be used to
-% access to the Tikz nodes created in the array from outside the environment. This variable is global for technical
-% reasons (some commands will be executed in an |\aftergroup| because we don't want to patch the commands of the
-% package \pkg{array}).
+% We don't want to patch any existing code. That's why some code must be executed in a |\aftergroup|. That's why
+% the parameters used in that code must be transfered outside the current group. To do this, we copy those
+% quantities in global variables just before the |\aftergroup|. Therefore, for those quantities, we have two
+% parameters, one local and one global. For example, we have |\l_@@_name_tl| and |\g_@@_name_tl|.
+%
+% \bigskip
+% The token list |\l_@@_name_tl| will contain the optional name of the environment: this name can be used to
+% access to the Tikz nodes created in the array from outside the environment. 
 %    \begin{macrocode}
 \tl_new:N \g_@@_name_tl
+\tl_new:N \l_@@_name_tl
+%    \end{macrocode}
+%
+% \bigskip
+% The boolean |\l_@@_extra_nodes_bool| will be used to indicate wether the ``medium nodes'' and ``large nodes'' are
+% created in the array. 
+%    \begin{macrocode}
+\bool_new:N \l_@@_extra_nodes_bool
+\bool_new:N \g_@@_extra_nodes_bool
+%    \end{macrocode}
+%
+% \bigskip
+% The dimensions |\l_@@_left_margin_dim| and |\l_@@_right_margin_dim| correspond to the options |left-margin| and |right-margin|.
+%    \begin{macrocode}
+\dim_new:N \l_@@_left_margin_dim
+\dim_new:N \l_@@_right_margin_dim
+\dim_new:N \g_@@_left_margin_dim
+\dim_new:N \g_@@_right_margin_dim
+%    \end{macrocode}
+%                              
+% \bigskip
+% The dimensions |\l_@@_extra_left_margin_dim| and |\l_@@_extra_right_margin_dim| correspond to the options
+% |extra-left-margin| and |extra-right-margin|. 
+%    \begin{macrocode}
+\dim_new:N \l_@@_extra_left_margin_dim
+\dim_new:N \l_@@_extra_right_margin_dim
+\dim_new:N \g_@@_extra_right_margin_dim
 %    \end{macrocode}
 % 
 % \bigskip
@@ -1458,8 +2067,7 @@ version 2005/12/01 or later.
 % With the option |renew-matrix|, the environment |{matrix}| of \pkg{amsmath} and its variants are redefined to
 % behave like the environment |{NiceMatrix}| and its variants.
 %    \begin{macrocode}
-      renew-matrix      .code:n     = {\cs_set_eq:NN \env@matrix \NiceMatrix
-                                      \bool_set_true:N \l_@@_renew_matrix_bool}, 
+      renew-matrix      .code:n     = \@@_renew_matrix:,
       renew-matrix      .value_forbidden:n = true,
       RenewMatrix       .meta:n     = renew-matrix,
       transparent       .meta:n     = {renew-dots,renew-matrix},
@@ -1477,17 +2085,6 @@ version 2005/12/01 or later.
       NullifyDots       .meta:n     = nullify-dots,
 %    \end{macrocode}
 %
-%
-% \bigskip
-% With the option |silent|, no error is generated for the impossible instructions. This option can be useful when
-% adapting an existing code. 
-%    \begin{macrocode}
-      silent            .code:n  = {\msg_redirect_name:nnn {nicematrix} 
-                                                           {Impossible~instruction}
-                                                           {none}} , 
-      silent            .value_forbidden:n = true,
-      Silent            .meta:n            = silent,
-%    \end{macrocode}
 % 
 % \bigskip
 % The following option is only for the environment |{pNiceArrayC}| and its variants. It will contain code inserted
@@ -1507,20 +2104,33 @@ version 2005/12/01 or later.
 %    \end{macrocode}
 %
 % \bigskip
-% If the option |columns-width| is used, all the columns will have the same width. In |\NiceMatrixOptions|, the
-% special value |auto| is not available.
+% If the option |columns-width| is used, all the columns will have the same width. 
+%
+% In |\NiceMatrixOptions|, the special value |auto| is not available.
+%    \begin{macrocode}
+      columns-width     .code:n    = \str_if_eq:nnTF {#1} {auto}
+                                     {\@@_msg_error:n {Option~auto~for~columns-width}}
+                                     {\dim_set:Nn \l_@@_columns_width_dim {#1}},
+%    \end{macrocode}
+%
+% \bigskip
 %    \begin{macrocode}
-      columns-width     .code:n      = \str_if_eq:nnTF {#1} {auto}
-                                           {\msg_error:nn {nicematrix} 
-                                                          {Option~auto~for~columns-width}}
-                                           {\dim_set:Nn \l_@@_columns_width_dim {#1}},
+      create-extra-nodes  .bool_set:N   = \l_@@_extra_nodes_bool,
+      create-extra-nodes  .default:n    = true,
 %    \end{macrocode}
 %
 % \bigskip
 %    \begin{macrocode}
-      unknown .code:n  = \msg_error:nn {nicematrix} {Unknown~key~for~NiceMatrixOptions}}
+      left-margin  .dim_set:N  = \l_@@_left_margin_dim,
+      left-margin  .default:n  = \arraycolsep,
+      right-margin .dim_set:N  = \l_@@_right_margin_dim,
+      right-margin  .default:n  = \arraycolsep,
 %    \end{macrocode}
 %
+% \bigskip
+%    \begin{macrocode}
+      unknown .code:n  = \@@_msg_error:n {Unknown~key~for~NiceMatrixOptions}}
+%    \end{macrocode}
 %    \begin{macrocode}
 \msg_new:nnnn {nicematrix}
               {Unknown~key~for~NiceMatrixOptions}
@@ -1531,10 +2141,12 @@ version 2005/12/01 or later.
               {The~available~keys~are~(in~alphabetic~order):~
                code-for-last-col,~
                exterior-arraycolsep,~
+               left-margin,~
                nullify-dots,~
                parallelize-diags,~
                renew-dots,~
-               renew-matrix~
+               renew-matrix,~
+               right-margin,~
                and~transparent}
 %    \end{macrocode}
 %
@@ -1564,7 +2176,7 @@ version 2005/12/01 or later.
       nullify-dots      .bool_set:N  = \l_@@_nullify_dots_bool ,
       nullify-dots      .default:n   = true,
 %    \end{macrocode}
-% The option |columns-width| is the width of the columns it we want the same width for all the columns of the
+% The option |columns-width| is the width of the columns if we want the same width for all the columns of the
 % array. A value of 0~pt means that the width of the column will be the natural width of the column.
 %    \begin{macrocode}
       columns-width     .code:n      = \str_if_eq:nnTF {#1} {auto}
@@ -1572,20 +2184,30 @@ version 2005/12/01 or later.
                                                 \l_@@_auto_columns_width_bool}
                                            {\dim_set:Nn \l_@@_columns_width_dim {#1}},
       name    .code:n                = {\seq_if_in:NnTF \g_@@_names_seq {#1}
-                                           {\msg_error:nnn {nicematrix}
-                                                           {Duplicate~name}
-                                                           {#1}}
+                                           {\@@_msg_error:nn {Duplicate~name} {#1}}
                                            {\seq_gput_left:Nn \g_@@_names_seq {#1}}
-                                        \tl_gset:Nn \g_@@_name_tl {#1}},
+                                        \tl_set:Nn \l_@@_name_tl {#1}},
       name    .value_required:n      = true,
-%    \end{macrocode}
-% Since we don't want to modify or patch any existing code, the ``code after'' will be inserted with an
-% |\aftergroup|. Thus, we can't use a local variable for the ``code after'' and that's why we use a global variable.
-%    \begin{macrocode}
-      code-after         .tl_gset:N    = \g_@@_code_after_tl,
+      code-after         .tl_set:N     = \l_@@_code_after_tl,
       code-after         .initial:n    = \c_empty_tl,
       code-after         .value_required:n = true,
-      unknown .code:n  = \msg_error:nn {nicematrix} {Unknown~option~for~NiceMatrix}}
+%    \end{macrocode}
+%
+% The key |create-extra-nodes| indicates wether the ``medium nodes'' and ``large nodes'' will be created for each
+% cell of the array. 
+%    \begin{macrocode}
+      create-extra-nodes  .bool_set:N   = \l_@@_extra_nodes_bool,
+      create-extra-nodes  .default:n    = true,
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+      left-margin  .dim_set:N  = \l_@@_left_margin_dim,
+      left-margin  .default:n  = \arraycolsep,
+      right-margin .dim_set:N  = \l_@@_right_margin_dim,
+      right-margin .default:n  = \arraycolsep,
+      extra-left-margin  .dim_set:N  = \l_@@_extra_left_margin_dim,
+      extra-right-margin .dim_set:N  = \l_@@_extra_right_margin_dim,
+      unknown .code:n  = \@@_msg_error:n {Unknown~option~for~NiceMatrix}}
 %    \end{macrocode}
 %
 %    \begin{macrocode}
@@ -1598,14 +2220,32 @@ version 2005/12/01 or later.
               {The~available~options~are~(in~alphabetic~order):~
                code-after,~
                columns-width,~
+               create-extra-nodes,~
+               extra-left-margin,~
+               extra-right-margin,~
+               left~margin,~
                name,~
                nullify-dots,~
-               parallelize-diags~
-               and~renew-dots.}
+               parallelize-diags,~
+               renew-dots~
+               and~right-margin.}
 %    \end{macrocode}
 % 
 % \bigskip
 %    \begin{macrocode}
+\msg_new:nnnn {nicematrix}
+              {Duplicate~name}
+              {The~name~"#1"~is~already~used~and~you~shouldn't~use~
+               the~same~environment~name~twice.~You~can~go~on,~but,~
+               maybe,~you~will~have~incorrect~results~especially~ 
+               if~you~use~"columns-width=auto".\\
+               For~a~list~of~the~names~already~used,~type~H~<return>.}
+              {The~names~already~defined~in~this~document~are:~
+               \seq_use:Nnnn~\g_@@_names_seq~{,~} {,~} {~and~}.}
+%    \end{macrocode}
+%
+% \bigskip
+%    \begin{macrocode}
 \keys_define:nn {NiceMatrix/NiceArray}
      {parallelize-diags    .bool_set:N = \l_@@_parallelize_diags_bool,
       parallelize-diags    .default:n  = true,
@@ -1613,18 +2253,14 @@ version 2005/12/01 or later.
       renew-dots           .default:n  = true,
       nullify-dots         .bool_set:N = \l_@@_nullify_dots_bool ,
       nullify-dots         .default:n  = true,
-      exterior-arraycolsep .bool_set:N = \l_@@_exterior_arraycolsep_bool ,
-      exterior-arraycolsep .default:n  = true,
-      columns-width        .code:n     = \str_if_eq:nnTF {#1} {auto}
-                                           {\bool_set_true:N \l_@@_auto_columns_width_bool}
-                                           {\dim_set:Nn \l_@@_columns_width_dim {#1}},
+      columns-width        .code:n = \str_if_eq:nnTF {#1} {auto}
+                                       {\bool_set_true:N \l_@@_auto_columns_width_bool}
+                                       {\dim_set:Nn \l_@@_columns_width_dim {#1}},
       columns-width        .value_required:n = true,
       name                 .code:n     = {\seq_if_in:NnTF \g_@@_names_seq {#1}
-                                            {\msg_error:nnn {nicematrix}
-                                                            {Duplicate~name}
-                                                            {#1}}
+                                            {\@@_msg_error:nn {Duplicate~name} {#1}}
                                             {\seq_gput_left:Nn \g_@@_names_seq {#1}}
-                                          \tl_gset:Nn \g_@@_name_tl {#1}},
+                                          \tl_set:Nn \l_@@_name_tl {#1}},
       name                 .value_required:n = true,
 %    \end{macrocode}
 % 
@@ -1635,10 +2271,18 @@ version 2005/12/01 or later.
       c                  .code:n    = \tl_set:Nn \l_@@_pos_env_tl c,
       t                  .code:n    = \tl_set:Nn \l_@@_pos_env_tl t,
       b                  .code:n    = \tl_set:Nn \l_@@_pos_env_tl b,
-      code-after         .tl_gset:N = \g_@@_code_after_tl,
+      code-after         .tl_set:N  = \l_@@_code_after_tl,
       code-after         .initial:n = \c_empty_tl,
       code-after         .value_required:n = true,
-      unknown .code:n  = \msg_error:nn {nicematrix} {Unknown~option~for~NiceArray}}
+      create-extra-nodes  .bool_set:N   = \l_@@_extra_nodes_bool,
+      create-extra-nodes  .default:n    = true,
+      left-margin  .dim_set:N  = \l_@@_left_margin_dim,
+      left-margin  .default:n  = \arraycolsep,
+      right-margin .dim_set:N  = \l_@@_right_margin_dim,
+      right-margin .default:n  = \arraycolsep,
+      extra-left-margin  .dim_set:N  = \l_@@_extra_left_margin_dim,
+      extra-right-margin .dim_set:N  = \l_@@_extra_right_margin_dim,
+      unknown .code:n  = \@@_msg_error:n {Unknown~option~for~NiceArray}}
 %    \end{macrocode}
 %
 %    \begin{macrocode}
@@ -1652,33 +2296,43 @@ version 2005/12/01 or later.
                b,~
                c,~
                code-after,~
+               create-extra-nodes,~
                columns-width,~
-               exterior-arraycolsep,~
+               extra-left-margin,~
+               extra-right-margin,~
+               left-margin,~
                name,~
                nullify-dots,~
                parallelize-diags,~
-               renew-dots~
+               renew-dots,~
+               right-margin,~
                and~t.}
 %    \end{macrocode}
 % 
 % \subsection{The environments \{NiceArray\} and \{NiceMatrix\}}
 %
-% The pseudo-environment |\@@_Cell:n|--|\@@_end_Cell:| will be used to format the cells of the array. In the code,
+% The pseudo-environment |\@@_Cell:|--|\@@_end_Cell:| will be used to format the cells of the array. In the code,
 % the affectations are global because this pseudo-environment will be used in the cells of a |\halign| (via an
 % environment |{array}|).
 %
-% The argument of |\@@_Cell:n| is a letter |l|, |c| or |r| that describes the type of column: we store this letter
-% at the end of |\g_@@_preamble_aux_tl| (see the redefinition of |\ialign| in the environment |{NiceArray}| for
-% explanations).
 %    \begin{macrocode}
-\cs_new_protected:Nn \@@_Cell:n
-   {\tl_gput_right:Nn \g_@@_preamble_aux_tl {#1}
+\cs_new_protected:Nn \@@_Cell:
+   { 
 %    \end{macrocode}
 % We increment |\g_@@_column_int|, which is the counter of the columns. 
 %    \begin{macrocode}
     \int_gincr:N \g_@@_column_int
+%    \end{macrocode}
+% Now, we increment the counter of the rows. We don't do this incrementation in the |\everycr| because some
+% packages, like \pkg{arydsln}, creates special rows in the |\halign| that we don't want to take into account.
+%    \begin{macrocode}
+    \int_compare:nNnT \g_@@_column_int = 1
+          {\int_gincr:N \g_@@_row_int}                
+    \int_gset:Nn \g_@@_column_total_int 
+                 {\int_max:nn \g_@@_column_total_int \g_@@_column_int}
     \hbox_set:Nw \l_tmpa_box $ % $ 
-          \l_@@_code_for_cell_tl } 
+    \int_compare:nNnT \g_@@_row_int = 0
+             \l_@@_code_for_first_row_tl}
 %    \end{macrocode}
 % 
 %    \begin{macrocode}
@@ -1692,20 +2346,31 @@ version 2005/12/01 or later.
 %    \begin{macrocode}
     \dim_gset:Nn \g_@@_max_cell_width_dim
           {\dim_max:nn \g_@@_max_cell_width_dim {\box_wd:N \l_tmpa_box}}
-   \tl_if_empty:NTF \g_@@_name_tl
-    {\tikz[remember~picture, inner~sep = 0pt, minimum~width = 0pt, baseline]
-       \node [anchor = base,
-              name = nm-\int_use:N \g_@@_env_int-
-                        \int_use:N \g_@@_row_int-
-                        \int_use:N \g_@@_column_int] }
-    {\tikz[remember~picture, inner~sep = 0pt, minimum~width = 0pt, baseline]
+%    \end{macrocode}
+%
+%
+%    \begin{macrocode}
+    \int_compare:nNnT \g_@@_row_int = 0
+       {\dim_gset:Nn \g_@@_max_dp_row_zero_dim
+            {\dim_max:nn \g_@@_max_dp_row_zero_dim {\box_dp:N \l_tmpa_box}}
+        \dim_gset:Nn \g_@@_max_ht_row_zero_dim
+            {\dim_max:nn \g_@@_max_ht_row_zero_dim {\box_ht:N \l_tmpa_box}}}
+    \int_compare:nNnT \g_@@_row_int = 1
+       {\dim_gset:Nn \g_@@_max_ht_row_one_dim
+            {\dim_max:nn \g_@@_max_ht_row_one_dim {\box_ht:N \l_tmpa_box}}}
+%    \end{macrocode}
+% 
+% Now, we can create the Tikz node of the cell.
+%    \begin{macrocode}
+    \tikz[remember~picture, inner~sep = 0pt, minimum~width = 0pt, baseline]
        \node [anchor = base,
               name = nm-\int_use:N \g_@@_env_int-
                         \int_use:N \g_@@_row_int-
                         \int_use:N \g_@@_column_int,
-              alias = \tl_use:N \g_@@_name_tl-
-                      \int_use:N \g_@@_row_int-
-                      \int_use:N \g_@@_column_int] }
+              alias = \tl_if_empty:NF \l_@@_name_tl
+                         {\tl_use:N \l_@@_name_tl-
+                          \int_use:N \g_@@_row_int-
+                          \int_use:N \g_@@_column_int} ] 
        \bgroup 
        \box_use:N \l_tmpa_box
        \egroup ;} 
@@ -1732,22 +2397,21 @@ version 2005/12/01 or later.
 % Here's the definition of |{NiceMatrix}|:
 %    \begin{macrocode}
 \NewDocumentEnvironment {NiceMatrix} {O{}}
-    {\bool_set_false:N \l_@@_direct_NiceArray_bool
-     \tl_gclear:N \g_@@_code_after_tl
-     \keys_set:nn {NiceMatrix/NiceMatrix} {#1}
+    {\keys_set:nn {NiceMatrix/NiceMatrix} {#1}
      \tl_set:Nn \l_@@_pos_env_tl c
      \bool_set_false:N \l_@@_exterior_arraycolsep_bool
          \NiceArray{*\c@MaxMatrixCols{C}}
       }
     {\endarray
-     \skip_horizontal:n {-\arraycolsep}}
+     \skip_horizontal:n {-\arraycolsep}
+     \skip_horizontal:n {\g_@@_right_margin_dim + \g_@@_extra_right_margin_dim}}
 %    \end{macrocode}
 %
 % \interitem
 % For the definition of |{NiceArray}| (just below), we have the following constraints:
 % \begin{itemize}
 % \item we must use |\array| in the first part of |{NiceArray}| and, therefore, |\endarray| in the second part;
-% \item we have to put a |\aftergroup \@@_draw_lines:| in the first part of |{NiceArray}| so that |\@@_draw_lines|
+% \item we have to put a |\aftergroup \@@_after_array:| in the first part of |{NiceArray}| so that |\@@_draw_lines|
 % will be executed at the end of the current environment (either |{NiceArray}| or |{NiceMatrix}|).
 % \end{itemize}
 %               
@@ -1755,15 +2419,25 @@ version 2005/12/01 or later.
 \cs_generate_variant:Nn \dim_set:Nn {Nx}
 %    \end{macrocode}
 % 
+%
+% \bigskip
+%    \begin{macrocode}
+\msg_new:nnn {nicematrix} 
+             {We~are~yet~in~an~environment~NiceArray}
+             {Environments~\{NiceArray\}~(or~\{NiceMatrix\},~etc.)~can't~be~
+              nested.~We~can~go~on,~but,~maybe,~you~will~have~errors~or~an~incorrect~
+              result.}
+%    \end{macrocode}
 % \bigskip
 % First, we test if we are yet in an environment |{NiceArray}| (nested environment are forbidden). It's easy to
 % test whether we are in an environment |{NiceArray}| : a special command |\@@_in_NiceArray:| is defined.
 %    \begin{macrocode}
 \NewDocumentEnvironment {NiceArray} {O{} m O{}}
     {\cs_if_exist:NT \@@_in_NiceArray:
-           {\msg_error:nn {nicematrix} {We~are~yet~in~an~environment~NiceArray}}
+           {\@@_msg_error:n {We~are~yet~in~an~environment~NiceArray}}
      \cs_set:Npn \@@_in_NiceArray: {--Void--}
-     \aftergroup \@@_draw_lines:
+     \aftergroup \@@_after_array:
+     \tl_gclear_new:N \g_@@_lines_to_draw_tl 
 %    \end{macrocode}
 %
 % We increment the counter |\g_@@_env_int| which counts the environments |{NiceArray}|.
@@ -1772,12 +2446,15 @@ version 2005/12/01 or later.
      \bool_if:NF \l_@@_block_auto_columns_width_bool
               {\dim_gzero_new:N \g_@@_max_cell_width_dim}
 %    \end{macrocode}
-% Maybe, an encompassing environment |{NiceMatrix}| or |{pNiceArrayC}| (for example) has already set the value for
-% |\g_@@_code_after_tl| (via the option |code-after|) and we don't want to erase this value. Thanks to the flag
-% |\l_@@_direct_NiceArray_bool|, it's possible.
+%
+% For the following variables, maybe we should create it only if we use the environment |{pNiceArrayRC}| or its variants.
+%    \begin{macrocode}
+     \dim_gzero_new:N \g_@@_max_dp_row_zero_dim
+     \dim_gzero_new:N \g_@@_max_ht_row_zero_dim
+     \dim_gzero_new:N \g_@@_max_ht_row_one_dim
+%    \end{macrocode}
+% 
 %    \begin{macrocode}
-     \bool_if:NT \l_@@_direct_NiceArray_bool
-              {\tl_gclear:N \g_@@_code_after_tl}
      \keys_set:nn {NiceMatrix/NiceArray} {#1,#3} 
 %    \end{macrocode}
 % 
@@ -1796,36 +2473,35 @@ version 2005/12/01 or later.
 % |_@@_name_cell_width|{\ttfamily\slshape name} (the value will be the correct value even if the number of the 
 % environment has changed (for example because the user has created or deleted an environment before the current one).
 %    \begin{macrocode}
-          \tl_if_empty:NF \g_@@_name_tl
-            {\cs_if_free:cF {_@@_max_cell_width_\g_@@_name_tl}
+          \tl_if_empty:NF \l_@@_name_tl
+            {\cs_if_free:cF {_@@_max_cell_width_\l_@@_name_tl}
                 {\dim_set:Nx \l_@@_columns_width_dim 
-                     {\use:c {_@@_max_cell_width_\g_@@_name_tl}}}}
+                     {\use:c {_@@_max_cell_width_\l_@@_name_tl}}}}
          }
 %    \end{macrocode}
+% We don't want to patch any code and that's why some code is excuted in a |\aftergroup|. In particular, in this
+% |\aftergroup|, we will have to know the value of some parameters like |\l_@@_extra_nodes_bool|. That's why we transit via a global
+% version for some variables.
+%    \begin{macrocode}
+     \bool_gset_eq:NN \g_@@_extra_nodes_bool \l_@@_extra_nodes_bool
+     \dim_gset_eq:NN \g_@@_left_margin_dim \l_@@_left_margin_dim
+     \dim_gset_eq:NN \g_@@_right_margin_dim \l_@@_right_margin_dim
+     \dim_gset_eq:NN \g_@@_extra_right_margin_dim \l_@@_extra_right_margin_dim
+     \tl_gset_eq:NN \g_@@_code_after_tl \l_@@_code_after_tl
+     \tl_gset_eq:NN \g_@@_name_tl \l_@@_name_tl
+%    \end{macrocode}
 % The environment |{array}| uses internally the command |\ialign| and, in particular, this command |\ialign| sets
-% |\everycr| to |{}|. However, we want to use |\everycr| in our array (in particular to increment |\g_@@_row_int|).
+% |\everycr| to |{}|. However, we want to use |\everycr| in our array.
 % The solution is to give to |\ialign| a new definition (giving to |\everycr| the value we want)
 % that will revert automatically to its default definition after the first utilisation.\footnote{With this programmation, we will
 % have, in the cells of the array, a clean version of |\ialign|. That's necessary: the user will probably not employ directly 
 % |\ialign| in the array...  but more likely environments that utilize |\ialign| internally (e.g.: |{substack}|)}
 %    \begin{macrocode}
      \cs_set:Npn \ialign 
-          {\everycr{\noalign{\int_gincr:N \g_@@_row_int
-                             \int_gzero:N \g_@@_column_int
-%    \end{macrocode}
-% We want to have the preamble of the array in |\g_@@_preamble_tl| at the end of the array. However, some rows of the array
-% may be shorter (that is to say without all the ampersands) and it's not possible to know which row will be the
-% longest. That's why, during the construction of a row, we retrieve the corresponding preamble in
-% |\g_@@_preamble_aux_tl|. At the end of the array, we are sure that the longest value will be the real preamble of
-% the array (stored in |\g_@@_preamble_tl|).
-%    \begin{macrocode}                                                                                  
-                             \int_compare:nNnT {\tl_count:N \g_@@_preamble_aux_tl}
-                                             > {\tl_count:N \g_@@_preamble_tl} 
-                                {\tl_gset_eq:NN \g_@@_preamble_tl \g_@@_preamble_aux_tl}
-                             \tl_gclear:N \g_@@_preamble_aux_tl}}
-          \skip_zero:N \tabskip
+          {\everycr{\noalign{\int_gzero:N \g_@@_column_int}}
+          \tabskip = \c_zero_skip
           \cs_set:Npn \ialign {\everycr{} 
-                               \skip_zero:N \tabskip
+                               \tabskip = \c_zero_skip
                                \halign}
           \halign}
 %    \end{macrocode}
@@ -1834,9 +2510,9 @@ version 2005/12/01 or later.
 % |{NiceArray}|.
 %    \begin{macrocode}
      \dim_compare:nNnTF \l_@@_columns_width_dim = \c_zero_dim
-        {\newcolumntype{L}{>{\@@_Cell:n l}l<{\@@_end_Cell:}}
-         \newcolumntype{C}{>{\@@_Cell:n c}c<{\@@_end_Cell:}}
-         \newcolumntype{R}{>{\@@_Cell:n r}r<{\@@_end_Cell:}}}
+        {\newcolumntype{L}{>{\@@_Cell:}l<{\@@_end_Cell:}}
+         \newcolumntype{C}{>{\@@_Cell:}c<{\@@_end_Cell:}}
+         \newcolumntype{R}{>{\@@_Cell:}r<{\@@_end_Cell:}}}
 %    \end{macrocode}
 % If there is an option that specify that all the columns must have the same width, the column types~|L|, |C|
 % and~|R| are in fact defined upon the column type~|w| of array which is, in fact, redefined below.
@@ -1857,14 +2533,14 @@ version 2005/12/01 or later.
 %    \begin{macrocode}
      \newcolumntype{w}[2]
        {>{\hbox_set:Nw \l_tmpa_box
-          \@@_Cell:n ##1}
+          \@@_Cell:}
         c
         <{\@@_end_Cell:
           \hbox_set_end:
           \makebox[##2][##1]{\box_use:N \l_tmpa_box}}}
      \newcolumntype{W}[2]
        {>{\hbox_set:Nw \l_tmpa_box
-          \@@_Cell:n ##1}
+          \@@_Cell:}
         c
         <{\@@_end_Cell:
           \hbox_set_end:
@@ -1880,29 +2556,19 @@ version 2005/12/01 or later.
      \cs_set_eq:NN \Ddots \@@_Ddots
      \cs_set_eq:NN \Iddots \@@_Iddots
      \cs_set_eq:NN \Hspace \@@_Hspace:
-     \cs_set_eq:NN \NiceMatrixEndPoint \@@_NiceMatrixEndPoint:
      \cs_set_eq:NN \Hdotsfor \@@_Hdotsfor
+     \cs_set_eq:NN \multicolumn \@@_multicolumn:nnn
      \bool_if:NT \l_@@_renew_dots_bool
         {\cs_set_eq:NN \ldots \@@_Ldots
          \cs_set_eq:NN \cdots \@@_Cdots
          \cs_set_eq:NN \vdots \@@_Vdots
          \cs_set_eq:NN \ddots \@@_Ddots
          \cs_set_eq:NN \iddots \@@_Iddots
+         \cs_set_eq:NN \dots \@@_Ldots
          \cs_set_eq:NN \hdotsfor \@@_Hdotsfor}
-     \bool_if:NF \l_@@_renew_matrix_bool
-       {\cs_set_eq:NN \multicolumn \@@_multicolumn:nn}
 %    \end{macrocode}
 % 
 %
-% We have to remind the types of the columns (|l|, |c| or |r|) because we will use this information when we will
-% draw the vertical dotted lines. That's why we store the types of the columns in |\g_@@_preamble_tl| (for example,
-% if the preamble of |{NiceArray}| is |L*4{C}R|, the final value of |\g_@@_preamble_tl| will be |lccccr| if the
-% user really uses the six columns).
-%    \begin{macrocode}
-     \tl_clear_new:N \g_@@_preamble_tl
-     \tl_clear_new:N \g_@@_preamble_aux_tl
-%    \end{macrocode}
-%
 % The sequence |\g_@@_empty_cells_seq| will contain a list of ``empty'' cells (not all the empty cells of the
 % matrix). If we want to indicate that the cell in row~$i$ and column~$j$ must be considered as empty, the token
 % list ``|i-j|'' will be put in this sequence.
@@ -1910,23 +2576,30 @@ version 2005/12/01 or later.
      \seq_gclear_new:N  \g_@@_empty_cells_seq
 %    \end{macrocode}
 %
-% The counter |\g_@@_instruction_int| will count the instructions (|\Cdots|, |\Vdots|, |\Ddots|, etc.) in the matrix.
+% The sequence |\g_@@_multicolumn_cells_seq| will contain the list of the cells of the array where a command
+% |\multicolumn{|$n$|}{...}{...}| with $n>1$ is issued. In |\g_@@_multicolumn_sizes_seq|, the ``sizes'' (that is to say
+% the values of $n$) correspondant will be stored. These lists will be used for the creation of the ``medium nodes''
+% (if they are created). 
 %    \begin{macrocode}
-     \int_gzero_new:N \g_@@_instruction_int
+     \seq_gclear_new:N \g_@@_multicolumn_cells_seq
+     \seq_gclear_new:N \g_@@_multicolumn_sizes_seq
 %    \end{macrocode}
+% 
 %
 % The counter |\g_@@_row_int| will be used to count the rows of the array (its incrementation will be in
-% |\everycr|). At the end of the environment |{array}|, this counter will give the total number of rows of the matrix.
+% the first cell of the row). At the end of the environment |{array}|, this counter will give the total number of
+% rows of the matrix. 
 %    \begin{macrocode}
      \int_gzero_new:N \g_@@_row_int 
-     \int_gset_eq:NN \g_@@_row_int \l_@@_number_of_first_row_int
+     \int_gset:Nn \g_@@_row_int {\l_@@_nb_first_row_int - 1}
 %    \end{macrocode}
 %
-% The counter |\g_@@_column_int| will be used to count the columns of the array (it will be set to zero in
-% |\everycr|). This counter is updated in the command |\@@_Cell:n| executed at the beginning of each cell. At the
-% end of the array (in the beginning of |\@@_draw_lines:|), it will be set to the total number of columns of the array.
+% The counter |\g_@@_column_int| will be used to count the columns of the array. Since we want to
+% know the total number of columns of the matrix, we also create a counter |\g_@@_column_total_int|.
+% These counters are updated in the command |\@@_Cell:| executed at the beginning of each cell. 
 %    \begin{macrocode}
      \int_gzero_new:N \g_@@_column_int 
+     \int_gzero_new:N \g_@@_column_total_int
      \cs_set_eq:NN \@ifnextchar \new@ifnextchar
 %    \end{macrocode}
 %
@@ -1939,7 +2612,12 @@ version 2005/12/01 or later.
          {\skip_horizontal:n {-\arraycolsep}}
 %    \end{macrocode}
 % 
-% Eventually, the environment |{NiceArray}| is defined upon the environment |{array}|. The token list |l_@@_pos_tl|
+%    \begin{macrocode}
+     \skip_horizontal:n {\l_@@_left_margin_dim + \l_@@_extra_left_margin_dim}
+%    \end{macrocode}
+% 
+% 
+% Eventually, the environment |{NiceArray}| is defined upon the environment |{array}|. The token list |\l_@@_pos_tl|
 % will contain one of the values |t|, |c| or |b|.
 %    \begin{macrocode}
      \array[\l_@@_pos_env_tl]{#2}}
@@ -1949,7 +2627,8 @@ version 2005/12/01 or later.
 %    \begin{macrocode}
     {\endarray
      \bool_if:NF \l_@@_exterior_arraycolsep_bool
-         {\skip_horizontal:n {-\arraycolsep}}}
+         {\skip_horizontal:n {-\arraycolsep}}
+     \skip_horizontal:n {\g_@@_right_margin_dim + \g_@@_extra_right_margin_dim}}
 %    \end{macrocode}
 %
 %
@@ -1996,22 +2675,22 @@ version 2005/12/01 or later.
 \cs_new_protected:Nn \@@_write_max_cell_width:
     {\bool_if:NF \l_@@_block_auto_columns_width_bool
        {\iow_now:Nn \@mainaux {\ExplSyntaxOn}
-        \iow_now:Nx \@mainaux {\cs_gset:cpn {_@@_max_cell_width_\int_use:N \g_@@_env_int} 
-                                            {\dim_use:N \g_@@_max_cell_width_dim} }
+        \iow_now:Nx \@mainaux {\cs_gset:cpn 
+                               {@@_max_cell_width_\int_use:N \g_@@_env_int}
+                               {\dim_use:N \g_@@_max_cell_width_dim} }
 %    \end{macrocode}
-% If the environment has a name, we also create an alias named |\_@@_max_cell_width_|{\ttfamily\slshape name}.
+% If the environment has a name, we also create an alias named |\@@_max_cell_width_|{\ttfamily\slshape name}.
 %    \begin{macrocode}
-          \iow_now:Nx \@mainaux {\cs_gset:cpn {_@@_max_cell_width_\g_@@_name_tl} 
+          \iow_now:Nx \@mainaux {\cs_gset:cpn {@@_max_cell_width_\g_@@_name_tl} 
                                               {\dim_use:N \g_@@_max_cell_width_dim} }
-        \iow_now:Nn \@mainaux {\ExplSyntaxOff}}
-     \tl_gclear:N \g_@@_name_tl}
+        \iow_now:Nn \@mainaux {\ExplSyntaxOff}}}
 %    \end{macrocode}
 % 
 % \interitem
 % The conditionnal |\@@_if_not_empty_cell:nnT| tests wether a cell is empty. The first two arguments must be LaTeX3
 % counters for the row and the column of the considered cell.
 %    \begin{macrocode}
-\prg_set_conditional:Npnn \@@_if_not_empty_cell:nn #1#2 {T}
+\prg_set_conditional:Npnn \@@_if_not_empty_cell:nn #1#2 {T,TF}
 %    \end{macrocode}
 % If the cell is an implicit cell (that is after the symbol |\\| of end of row), the cell must, of course, be
 % considered as empty. It's easy to check wether we are in this situation considering the correspondant Tikz node.
@@ -2045,83 +2724,76 @@ version 2005/12/01 or later.
                 \dim_gset:Nn \g_tmpb_dim \pgf@x
               \end{pgfpicture}
               \dim_compare:nNnTF {\dim_abs:n {\g_tmpb_dim-\g_tmpa_dim}} < {0.5 pt}
-                    {\prg_return_false:}
-                    {\prg_return_true:}
+                    \prg_return_false:
+                    \prg_return_true:
              }}
-          {\prg_return_false:}
+          \prg_return_false:
        }
 %    \end{macrocode}
 %
-% \interitem
-% For each drawing instruction in the matrix (like |\Cdots|, etc.), we create a global property list to store the
-% informations corresponding to the instruction. Such an property list will have three fields:
-% \begin{itemize}
-% \item a field ``type'' with the type of the instruction (|cdots|, |vdots|, |ddots|, etc.);
-% \item a field ``row'' with the number of the row of the matrix where the instruction appeared;
-% \item a field ``column'' with the number of the column of the matrix where the instruction appeared.
-% \end{itemize}
+% \interitem
+% The argument of the following command |\@@_instruction_of_type:n| is the type of the instruction (|Cdots|,
+% |Vdots|, |Ddots|, etc.). This command writes in |\g_@@_lines_to_draw_tl| the instruction that will really draw
+% the line after the construction of the matrix.
+%
+% \medskip
+% For example, for the following matrix,
+% 
+% \smallskip
+% \begin{BVerbatim}[baseline=c,boxwidth=11cm]
+% \begin{pNiceMatrix}
+% 1 & 2 & 3 & 4 \\
+% 5 & \Cdots & & 6 \\
+% 7 & \Hdotsfor{2} \\
+% \end{pNiceMatrix}
+% \end{BVerbatim}
+% $\begin{pNiceMatrix}
+% 1 & 2 & 3 & 4 \\
+% 5 & \Cdots & & 6 \\
+% 7 & \Hdotsfor{2} \\
+% \end{pNiceMatrix}$
+%
+% the content of |\g_@@_lines_to_draw_tl| will be:
+% 
+% \begin{scope}
+% \color{gray}
+% \verb|\@@_draw_Cdots:nn {2}{2}|
 %
-% \interitem
-% The argument of the following command |\@@_instruction_of_type:n| is the type of the instruction (|cdots|,
-% |vdots|, |ddots|, etc.). This command creates the corresponding property list.
+% \verb|\@@_draw_Hdotsfor:nnn {3}{2}{2}|
+% \end{scope} 
+% 
 %    \begin{macrocode}
 \cs_new_protected:Nn \@@_instruction_of_type:n 
-%    \end{macrocode}
-% First, we increment the counter of the instructions (this counter is initialized in the beginning of the
-% environment |{NiceMatrix}|). This incrementation is global because the command will be used in the cell of a |\halign|).
-%    \begin{macrocode}
-     {\int_gincr:N \g_@@_instruction_int
-      \prop_put:Nnn \l_tmpa_prop {type} {#1}
-      \prop_put:NnV \l_tmpa_prop {row} \g_@@_row_int
-      \prop_put:NnV \l_tmpa_prop {column} \g_@@_column_int
-%    \end{macrocode}
-% The property list has been created in a local variable for convenience. Now, it will be stored in a
-% global variable indicating the number of the instruction.
-%    \begin{macrocode}
-      \prop_gclear_new:c 
-         {g_@@_instruction_\int_use:N\g_@@_instruction_int _prop}
-      \prop_gset_eq:cN
-         {g_@@_instruction_\int_use:N\g_@@_instruction_int _prop}
-         \l_tmpa_prop
-      }
+     {\tl_gput_right:Nx \g_@@_lines_to_draw_tl 
+           {\exp_not:c {@@_draw_#1:nn} 
+                       {\int_use:N \g_@@_row_int} 
+                       {\int_use:N \g_@@_column_int}}}
 %    \end{macrocode}
 %
 % 
-% \subsection{We draw the lines in the matrix}
+% \subsection{After the construction of the array}
 %
 %    \begin{macrocode}
-\cs_new_protected:Nn \@@_draw_lines:
+\cs_new_protected:Nn \@@_after_array:
     {
 %    \end{macrocode}
-% The last |\cr| in the array has incremented the counter |\g_@@_row_int|. That's why we decrement it to have the
-% real number of rows.
-%    \begin{macrocode}
-     \int_decr:N \g_@@_row_int
-%    \end{macrocode}
-% The counter |\g_@@_column_int| will now be the total number of columns in the array.                           
+% Now, the definition of the counters |\g_@@_column_int| and |\g_@@_column_total_int| change: |\g_@@_column_int|
+% will be the number of columns without the exterior column (in an environment like |{pNiceArrayC}|) and
+% |\g_@@_column_total_int| will be the number of columns with this exterior column.
 %    \begin{macrocode}
-     \int_set:Nn \g_@@_column_int {\tl_count:N \g_@@_preamble_tl}
+     \int_gset_eq:NN \g_@@_column_int \g_@@_column_total_int
+     \bool_if:NT \l_@@_exterior_column_bool {\int_gdecr:N \g_@@_column_int} 
 %    \end{macrocode}
 %
-% The sequence |\l_@@_yet_drawn_seq| contains a list of lines which have been drawn previously in the matrix. We
+% The sequence |\g_@@_yet_drawn_seq| contains a list of lines which have been drawn previously in the matrix. We
 % maintain this sequence because we don't want to draw two overlapping lines.
 %    \begin{macrocode}
-     \seq_clear_new:N \l_@@_yet_drawn_seq
-%    \end{macrocode}
-%
-%
-% The following variables will be used further.
-%    \begin{macrocode}
-     \int_zero_new:N \l_@@_type_int
-     \int_zero_new:N \l_@@_row_int
-     \int_zero_new:N \l_@@_column_int
-     \int_zero_new:N \l_@@_di_int
-     \int_zero_new:N \l_@@_dj_int
+     \seq_gclear_new:N \g_@@_yet_drawn_seq
 %    \end{macrocode}
 %
-% By befault, the diagonal lines will be parallelized\footnote{It's possible to use the option
+% By default, the diagonal lines will be parallelized\footnote{It's possible to use the option
 % |parallelize-diags| to disable this parallelization.}. There are two types of diagonals lines: the $|\Ddots|$
-% diagonals and the |\Iddots| diagonals. We have to count both types in order to known wether a diagonal is the
+% diagonals and the |\Iddots| diagonals. We have to count both types in order to know wether a diagonal is the
 % first of its type in the current |{NiceArray}| environment.
 %    \begin{macrocode}
      \bool_if:NT \l_@@_parallelize_diags_bool
@@ -2139,185 +2811,179 @@ version 2005/12/01 or later.
            \dim_zero_new:N \l_@@_delta_x_two_dim
            \dim_zero_new:N \l_@@_delta_y_two_dim}
 %    \end{macrocode}
-% 
-% \interitem
-% The counter |\l_@@_instruction_int| will be the index of the loop over the instructions. The first value is~$1$.
+%
+% If the user has used the option |create-extra-nodes|, the ``medium nodes'' and ``large nodes'' are created. We
+% recall that the command |\@@_create_extra_nodes:|, when used once, becomes no-op (in the current TeX group).
 %    \begin{macrocode}
-     \int_zero_new:N \l_@@_instruction_int
-     \int_incr:N \l_@@_instruction_int
+     \bool_if:NT \g_@@_extra_nodes_bool \@@_create_extra_nodes:
 %    \end{macrocode}
-%
-% \interitem
-% We begin the loop over the instructions (the incrementation is at the end of the loop).
+% 
+% \bigskip
+% Now, we really draw the lines. The code to draw the lines has been constructed in the token list |\g_@@_lines_to_draw_tl|.
 %    \begin{macrocode}
-     \int_until_do:nNnn \l_@@_instruction_int > \g_@@_instruction_int
-        {
+     \tl_if_empty:NF \g_@@_lines_to_draw_tl
+           {\int_zero_new:N  \l_@@_initial_i_int
+            \int_zero_new:N  \l_@@_initial_j_int
+            \int_zero_new:N  \l_@@_final_i_int
+            \int_zero_new:N  \l_@@_final_j_int
+            \@@_bool_new:N \l_@@_initial_open_bool
+            \@@_bool_new:N \l_@@_final_open_bool
+            \g_@@_lines_to_draw_tl}
+     \tl_gclear:N \g_@@_lines_to_draw_tl
 %    \end{macrocode}
 %
-% \interitem
-% We extract from the property list of the current instruction the fields ``type'', ``row'' and ``column'' and we
-% store these values. We have to do a conversion because the components of a property list are token lists (and not
-% integers).
+% \bigskip
+% Now, the |code-after|.
 %    \begin{macrocode}
-         \prop_get:cnN {g_@@_instruction_\int_use:N \l_@@_instruction_int _prop}
-                        {type} \l_tmpa_tl
-         \int_set:Nn \l_@@_type_int {\l_tmpa_tl}
-         \prop_get:cnN {g_@@_instruction_\int_use:N \l_@@_instruction_int _prop}
-                        {row} \l_tmpa_tl
-         \int_set:Nn \l_@@_row_int {\l_tmpa_tl}
-         \prop_get:cnN {g_@@_instruction_\int_use:N \l_@@_instruction_int _prop}
-                        {column} \l_tmpa_tl
-         \int_set:Nn \l_@@_column_int {\l_tmpa_tl}
+     \group_begin:
+     \tikzset{every~picture/.style = {overlay,
+                                      remember~picture,
+                                      name~prefix = nm-\int_use:N \g_@@_env_int-}}
+     \cs_set_eq:NN \line \@@_line:nn
+     \g_@@_code_after_tl 
+     \group_end:}
 %    \end{macrocode}
 %
-% \interitem
-% We fix the values of |\l_@@_di_int| and |\l_@@_dj_int| which indicate the direction of the dotted line to draw in
-% the matrix.
-%    \begin{macrocode}
-           \int_case:nn \l_@@_type_int
-             { 0 {\int_set:Nn \l_@@_di_int 0
-                  \int_set:Nn \l_@@_dj_int 1}
-               1 {\int_set:Nn \l_@@_di_int 0
-                  \int_set:Nn \l_@@_dj_int 1}
-               2 {\int_set:Nn \l_@@_di_int 1
-                  \int_set:Nn \l_@@_dj_int 0}
-               3 {\int_set:Nn \l_@@_di_int 1
-                  \int_set:Nn \l_@@_dj_int 1}
-               4 {\int_set:Nn \l_@@_di_int 1
-                  \int_set:Nn \l_@@_dj_int {-1}}}
-%    \end{macrocode}
+% \bigskip
+% A dotted line will be said \emph{open} in one of its extremity when it stops on the edge of the matrix and \emph{closed}
+% otherwise. In the following matrix, the dotted line is closed on its left extremity and open on its right.
+% \[ \begin{pNiceMatrix}
+% a+b+c & a+b & a\\
+% a & \Cdots \\
+% a & a+b & a+b+c
+% \end{pNiceMatrix}\]
+% For a closed extremity, we use the normal node and for a open one, we use the ``medium node'' (the medium and
+% large nodes are created with |\@@_create_extra_nodes:| if they have not been created yet).
+% \[ \begin{pNiceMatrix}[code-after = {\begin{tikzpicture} 
+%                                      \node [highlight, fit={(2-1)}] {} ;
+%                                      \node [highlight, fit={(2-3-medium)}] {} ;
+%                                      \end{tikzpicture}
+%                                    }]
+% a+b+c & a+b & a\\
+% a & \Cdots \\
+% a & a+b & a+b+c
+% \end{pNiceMatrix}\]
 %
-% \interitem 
-% An instruction for a dotted line must have a initial cell and a final cell which are both not empty. If it's not
-% the case, the instruction is said \emph{impossible}. An error will be raised if an impossible instruction is
-% encountered.
-%    \begin{macrocode}
-           \bool_if_exist:NTF \l_@@_impossible_instruction_bool
-               {\bool_set_false:N \l_@@_impossible_instruction_bool}
-               {\bool_new:N \l_@@_impossible_instruction_bool}
-%    \end{macrocode}
+% 
+% \bigskip
+% The command |\@@_find_extremities_of_line:nnnn| takes four arguments:
 %
-% \interitem
-% We will determine |\l_@@_final_i_int| and |\l_@@_final_j_int| which will be the ``coordinates'' of the end of the
-% dotted line we have to draw.
-%    \begin{macrocode}
-           \int_zero_new:N  \l_@@_final_i_int
-           \int_zero_new:N  \l_@@_final_j_int
-           \int_set:Nn \l_@@_final_i_int \l_@@_row_int
-           \int_set:Nn \l_@@_final_j_int \l_@@_column_int
-           \bool_if_exist:NTF \l_@@_stop_loop_bool
-                  {\bool_set_false:N \l_@@_stop_loop_bool}
-                  {\bool_new:N \l_@@_stop_loop_bool}
+% \begin{itemize}
+% \item the first argument is the row of the cell where the command was issued;
+% \item the second argument is the column of the cell where the command was issued;
+% \item the third argument is the $x$-value of the orientation vector of the line;
+% \item the fourth argument is the $y$-value the orientation vector of the line;
+% \end{itemize}
+%
+% This command computes:
+%
+% \begin{itemize}
+% \item |\l_@@_initial_i_int| and |\l_@@_initial_j_int| which are the coordinates of one extremity of the line;
+% \item |\l_@@_final_i_int| and |\l_@@_final_j_int| which are the coordinates of the other extremity of the line;
+% \item |\l_@@_initial_open_bool| and |\l_@@_final_open_bool| to indicate wether the extremities are open or not.
+% \end{itemize}
+%
+%    \begin{macrocode}       
+\cs_new_protected:Nn \@@_find_extremities_of_line:nnnn
+          {\int_set:Nn \l_@@_initial_i_int {#1}
+           \int_set:Nn \l_@@_initial_j_int {#2}
+           \int_set:Nn \l_@@_final_i_int {#1}
+           \int_set:Nn \l_@@_final_j_int {#2}
+           \bool_set_false:N \l_@@_initial_open_bool
+           \bool_set_false:N \l_@@_final_open_bool
+%    \end{macrocode}
+% We will do two loops: one when determinating the initial cell and the other when determinating the final cell. 
+% The boolean |\l_@@_stop_loop_bool| will be used to control these loops.
+%    \begin{macrocode}
+           \@@_bool_new:N \l_@@_stop_loop_bool
            \bool_do_until:Nn \l_@@_stop_loop_bool 
-              {\int_add:Nn \l_@@_final_i_int \l_@@_di_int
-               \int_add:Nn \l_@@_final_j_int \l_@@_dj_int
+              {\int_add:Nn \l_@@_final_i_int {#3}
+               \int_add:Nn \l_@@_final_j_int {#4}
 %    \end{macrocode}
 % We test if we are still in the matrix. 
 %    \begin{macrocode}
-               \bool_if:nTF { \int_compare_p:nNn \l_@@_final_i_int < \l_@@_number_of_first_row_int
-                           || \int_compare_p:nNn \l_@@_final_i_int > \g_@@_row_int
-                           || \int_compare_p:nNn \l_@@_final_j_int < 1
-                           || \int_compare_p:nNn \l_@@_final_j_int > \g_@@_column_int}
+               \bool_if:nTF { \int_compare_p:nNn 
+                                  \l_@@_final_i_int < {\l_@@_nb_first_row_int - 1}
+                           || \int_compare_p:nNn 
+                                  \l_@@_final_i_int > \g_@@_row_int
+                           || \int_compare_p:nNn 
+                                  \l_@@_final_j_int < 1
+                           || \int_compare_p:nNn 
+                                  \l_@@_final_j_int > \g_@@_column_total_int}
 %    \end{macrocode}
-% If we are outside the matrix, the instruction is impossible and, of course, we stop the loop.
+% If we are outside the matrix, we have found the extremity of the dotted line and it's a \emph{open} extremity.
 %    \begin{macrocode}
-                       {\bool_set_true:N \l_@@_impossible_instruction_bool
+                       {\bool_set_true:N \l_@@_final_open_bool
+%    \end{macrocode}
+% We do a step backwards because we will draw the dotted line upon the last cell in the matrix (we will use the
+% ``medium node'' of this cell).
+%    \begin{macrocode}  
+                        \int_sub:Nn \l_@@_final_i_int {#3}
+                        \int_sub:Nn \l_@@_final_j_int {#4}
                         \bool_set_true:N \l_@@_stop_loop_bool}
 %    \end{macrocode}
 % If we are in the matrix, we test if the cell is empty. If it's not the case, we stop the loop because we have
 % found the correct values for |\l_@@_final_i_int| and |\l_@@_final_j_int|.
 %    \begin{macrocode}
-                       {\@@_if_not_empty_cell:nnT \l_@@_final_i_int \l_@@_final_j_int
+                       {\@@_if_not_empty_cell:nnT 
+                              \l_@@_final_i_int 
+                              \l_@@_final_j_int
                               {\bool_set_true:N \l_@@_stop_loop_bool}}
                }
 %    \end{macrocode}
 % 
 % \interitem
-% We will determine |\l_@@_initial_i_int| and |\l_@@_initial_j_int| which will be the ``coordinates'' of the
-% beginning of the dotted line we have to draw. The programmation is similar to the previous one.
-%    \begin{macrocode}
-           \int_zero_new:N  \l_@@_initial_i_int
-           \int_zero_new:N  \l_@@_initial_j_int
-           \int_set:Nn \l_@@_initial_i_int \l_@@_row_int
-           \int_set:Nn \l_@@_initial_j_int \l_@@_column_int
-%    \end{macrocode}
-% If we know that the instruction is impossible (because it was not possible to found the correct value for 
-% |\l_@@_final_i_int| and |\l_@@_final_j_int|), we don't do this loop.
+% For |\l_@@_initial_i_int| and |\l_@@_initial_j_int| the programmation is similar to the previous one.
 %    \begin{macrocode}
-           \bool_set_eq:NN \l_@@_stop_loop_bool \l_@@_impossible_instruction_bool
+           \bool_set_false:N \l_@@_stop_loop_bool
            \bool_do_until:Nn \l_@@_stop_loop_bool 
-              {\int_sub:Nn \l_@@_initial_i_int \l_@@_di_int
-               \int_sub:Nn \l_@@_initial_j_int \l_@@_dj_int
+              {\int_sub:Nn \l_@@_initial_i_int {#3}
+               \int_sub:Nn \l_@@_initial_j_int {#4}
                \bool_if:nTF 
-                       {   \int_compare_p:nNn \l_@@_initial_i_int < \l_@@_number_of_first_row_int
-                        || \int_compare_p:nNn \l_@@_initial_i_int > \g_@@_row_int
-                        || \int_compare_p:nNn \l_@@_initial_j_int < 1
-                        || \int_compare_p:nNn \l_@@_initial_j_int > \g_@@_column_int}
-                       {\bool_set_true:N \l_@@_impossible_instruction_bool
+                       {   \int_compare_p:nNn 
+                               \l_@@_initial_i_int < \l_@@_nb_first_row_int
+                        || \int_compare_p:nNn 
+                               \l_@@_initial_i_int > \g_@@_row_int
+                        || \int_compare_p:nNn 
+                               \l_@@_initial_j_int < 1
+                        || \int_compare_p:nNn 
+                               \l_@@_initial_j_int > \g_@@_column_total_int}
+                       {\bool_set_true:N \l_@@_initial_open_bool
+                        \int_add:Nn \l_@@_initial_i_int {#3}
+                        \int_add:Nn \l_@@_initial_j_int {#4}
                         \bool_set_true:N \l_@@_stop_loop_bool}
-                       {\@@_if_not_empty_cell:nnT \l_@@_initial_i_int \l_@@_initial_j_int
+                       {\@@_if_not_empty_cell:nnT 
+                              \l_@@_initial_i_int 
+                              \l_@@_initial_j_int
                               {\bool_set_true:N \l_@@_stop_loop_bool}}
                }
 %    \end{macrocode}
-%
-% \interitem
-% Now, we can determine wether we have to draw a line. 
-% If the line is impossible, of course, we won't draw any line.
+% If we have at least one open extremity, we create the ``medium nodes'' in the matrix (in the case of an open
+% extremity, the dotted line uses the ``medium node'' of the last empty cell). We remind that, when used once, the
+% command |\@@_create_extra_nodes:| becomes no-op in the current TeX group.
 %    \begin{macrocode}
-          \bool_if:NTF \l_@@_impossible_instruction_bool
-            {\msg_error:nn {nicematrix} {Impossible~instruction}}
+           \bool_if:nT {\l_@@_initial_open_bool || \l_@@_final_open_bool}
+                       \@@_create_extra_nodes: }
 %    \end{macrocode}
 %
-% If the dotted line to draw is in the list of the previously drawn lines (|\l_@@_yet_drawn_seq|), we don't draw
+% \interitem
+% If the dotted line to draw is in the list of the previously drawn lines (|\g_@@_yet_drawn_seq|), we don't draw
 % (so, we won't have overlapping lines in the \textsc{pdf}). The token list |\l_tmpa_tl| is the $4$-uplet
 % characteristic of the line.
 %    \begin{macrocode}
+\prg_set_conditional:Npnn \@@_if_yet_drawn: {F}
             {\tl_set:Nx \l_tmpa_tl {\int_use:N \l_@@_initial_i_int-
                                     \int_use:N \l_@@_initial_j_int-
                                     \int_use:N \l_@@_final_i_int-
                                     \int_use:N \l_@@_final_j_int}
-             \seq_if_in:NVF \l_@@_yet_drawn_seq \l_tmpa_tl
-%    \end{macrocode}
-%
-% If the dotted line to draw is not in the list, we add it the list |\l_@@_yet_drawn_seq|.
-%    \begin{macrocode}
-              {\seq_put_left:NV \l_@@_yet_drawn_seq \l_tmpa_tl
-%    \end{macrocode}
-%
-% \medskip
-% The four following variables are global because we will have to do affectations in a Tikz instruction (in order
-% to extract the coordinates of two extremities of the line to draw).
-%    \begin{macrocode}
-               \dim_zero_new:N \g_@@_x_initial_dim 
-               \dim_zero_new:N \g_@@_y_initial_dim 
-               \dim_zero_new:N \g_@@_x_final_dim 
-               \dim_zero_new:N \g_@@_y_final_dim
-%    \end{macrocode}
-%
-% 
-% We draw the line.
-%    \begin{macrocode}
-               \int_case:nn \l_@@_type_int 
-                {0  \@@_draw_ldots_line:
-                 1  \@@_draw_cdots_line:
-                 2  \@@_draw_vdots_line:
-                 3  \@@_draw_ddots_line:
-                 4  \@@_draw_iddots_line:}}}
+             \seq_if_in:NVTF \g_@@_yet_drawn_seq \l_tmpa_tl
 %    \end{macrocode}
 %
-% \bigskip
-% Incrementation of the index of the loop (and end of the loop).
+% If the dotted line to draw is not in the list, we add it to the list |\g_@@_yet_drawn_seq|.
 %    \begin{macrocode}
-            \int_incr:N \l_@@_instruction_int
-         }
-     \group_begin:
-     \tikzset{every~picture/.style = {overlay,
-                                      remember~picture,
-                                      name~prefix = nm-\int_use:N \g_@@_env_int-}}
-     \cs_set_eq:NN \line \@@_line:nn
-     \g_@@_code_after_tl 
-     \group_end:
-}
+              {\prg_return_true:}
+              {\seq_gput_left:NV \g_@@_yet_drawn_seq \l_tmpa_tl
+               \prg_return_false:}}
 %    \end{macrocode}
 %
 %
@@ -2327,74 +2993,123 @@ version 2005/12/01 or later.
 % adjustment of one of the coordinates may be done.}. This command has four implicit arguments which are
 % |\l_@@_initial_i_int|, |\l_@@_initial_j_int|, |\l_@@_final_i_int| and |\l_@@_final_j_int|.
 %
-% The two arguments of the command |\@@_retrieve_coords:nn| are the anchors that must be used for the two nodes.
+% The two arguments of the command |\@@_retrieve_coords:nn| are the prefix and the anchor that must be used for the
+% two nodes. 
 %
 % The coordinates are stored in |\g_@@_x_initial_dim|, |\g_@@_y_initial_dim|, |\g_@@_x_final_dim|,
 % |\g_@@_y_final_dim|. These variables are global for technical reasons: we have to do an affectation in an
-% environment |{pgfpicture}|.
+% environment |{tikzpicture}|.
 %    \begin{macrocode}
 \cs_new_protected:Nn \@@_retrieve_coords:nn
-     {\begin{tikzpicture}[remember~picture]
+     {\dim_gzero_new:N \g_@@_x_initial_dim 
+      \dim_gzero_new:N \g_@@_y_initial_dim 
+      \dim_gzero_new:N \g_@@_x_final_dim 
+      \dim_gzero_new:N \g_@@_y_final_dim
+      \begin{tikzpicture}[remember~picture]
       \tikz@parse@node\pgfutil@firstofone
              (nm-\int_use:N \g_@@_env_int-
                  \int_use:N \l_@@_initial_i_int-
-                 \int_use:N \l_@@_initial_j_int.#1)
+                 \int_use:N \l_@@_initial_j_int #1)
       \dim_gset:Nn \g_@@_x_initial_dim \pgf@x
       \dim_gset:Nn \g_@@_y_initial_dim \pgf@y
       \tikz@parse@node\pgfutil@firstofone
              (nm-\int_use:N \g_@@_env_int-
                  \int_use:N \l_@@_final_i_int-
-                 \int_use:N \l_@@_final_j_int.#2)
+                 \int_use:N \l_@@_final_j_int #2)
       \dim_gset:Nn \g_@@_x_final_dim \pgf@x
       \dim_gset:Nn \g_@@_y_final_dim \pgf@y
       \end{tikzpicture} }
+\cs_generate_variant:Nn \@@_retrieve_coords:nn {xx}
 %    \end{macrocode}
 %
 % \interitem
 %    \begin{macrocode}
-\cs_new_protected:Nn \@@_draw_ldots_line:
-      {\@@_retrieve_coords:nn {south~east} {south~west}
-       \@@_draw_tikz_line:}
+\cs_new_protected:Nn \@@_draw_Ldots:nn
+      {\@@_find_extremities_of_line:nnnn {#1} {#2} 0 1 
+       \@@_if_yet_drawn:F \@@_actually_draw_Ldots:}
 %    \end{macrocode}
-%
-% \bigskip
-%    \begin{macrocode}
-\cs_new_protected:Nn \@@_draw_cdots_line:
-      {\@@_retrieve_coords:nn {mid~east} {mid~west}
-       \@@_draw_tikz_line:}
-%    \end{macrocode}
-%
-% \bigskip
-% For the vertical dotted lines, there is a problem because we want really vertical lines. If the type of the
-% column is |c| (from a type |C| in |{NiceArray}|), all the Tikz nodes of the column have the same $x$-value for the
-% anchors |south| and |north|. However, if the type of the column is |l| or |r| (from a type |L| or |R| in
-% |{NiceArray}|), the geometric line from the anchors |south| and |north| would probably not be really vertical.
-% That's why we need to known the type of the column and that's why we have constructed a token list
-% |\g_@@_preamble_tl| to store the types (|l|, |c| or |r|) of all the columns.
-%    \begin{macrocode}
-\cs_new_protected:Nn \@@_draw_vdots_line:
-      {\@@_retrieve_coords:nn {south} {north}
-%    \end{macrocode}
-% We store in |\t_tmpa_tl| the type of the column (|l|, |c| or |r|).
-%    \begin{macrocode}
-       \tl_set:Nx \l_tmpa_tl {\tl_item:Nn \g_@@_preamble_tl \l_@@_initial_j_int}
-%    \end{macrocode}
-% If the column is of type |l|, we will draw the dotted line on the left-most abscissa.
+% 
+% \medskip
+% The command |\@@_actually_draw_Ldots:| actually draws the |Ldots| line using |\l_@@_initial_i_int|,
+% |\l_@@_initial_j_int|, |\l_@@_initial_open_bool|, |\l_@@_final_i_int|, |\l_@@_final_j_int| and
+% |\l_@@_final_open_bool|. We have a dedicated command because if is used also by |\Hdotsfor|.
+%    \begin{macrocode}
+\cs_new_protected:Nn \@@_actually_draw_Ldots:
+          {\@@_retrieve_coords:xx {\bool_if:NTF \l_@@_initial_open_bool
+                                     {-medium.base~west}
+                                     {.base~east}} 
+                                  {\bool_if:NTF \l_@@_final_open_bool 
+                                     {-medium.base~east}
+                                     {.base~west}}
+           \bool_if:NT \l_@@_initial_open_bool
+                 {\dim_gset_eq:NN \g_@@_y_initial_dim \g_@@_y_final_dim }
+           \bool_if:NT \l_@@_final_open_bool                 
+                 {\dim_gset_eq:NN \g_@@_y_final_dim \g_@@_y_initial_dim }
+%    \end{macrocode}
+% We raise the line of a quantity equal to the radius of the dots because we want the dots really ``on'' the line
+% of texte.
+%    \begin{macrocode}
+           \dim_gadd:Nn \g_@@_y_initial_dim {0.53pt}
+           \dim_gadd:Nn \g_@@_y_final_dim {0.53pt}
+           \@@_draw_tikz_line:}
+%    \end{macrocode}
+%
+% \bigskip
+%    \begin{macrocode}
+\cs_new_protected:Nn \@@_draw_Cdots:nn
+      {\@@_find_extremities_of_line:nnnn {#1} {#2} 0 1 
+       \@@_if_yet_drawn:F
+            {\@@_retrieve_coords:xx {\bool_if:NTF \l_@@_initial_open_bool
+                                        {-medium.mid~west}
+                                        {.mid~east}} 
+                                    {\bool_if:NTF \l_@@_final_open_bool
+                                        {-medium.mid~east}
+                                        {.mid~west}}
+             \bool_if:NT \l_@@_initial_open_bool
+                   {\dim_gset_eq:NN \g_@@_y_initial_dim \g_@@_y_final_dim }
+             \bool_if:NT \l_@@_final_open_bool                 
+                   {\dim_gset_eq:NN \g_@@_y_final_dim \g_@@_y_initial_dim }
+             \@@_draw_tikz_line:}}
+%    \end{macrocode}
+%
+% \bigskip
+% For the vertical dots, we have to distinguish different instances because we want really vertical lines. Be
+% careful: it's not possible to insert the command |\@@_retrieve_coords:nn| in the arguments |T| and |F| of the
+% \pkg{expl3} commands (why?).
 %    \begin{macrocode}      
-       \str_if_eq:VnT \l_tmpa_tl {l}
-            {\dim_set:Nn \g_@@_x_initial_dim {\dim_min:nn \g_@@_x_initial_dim \g_@@_x_final_dim}
-             \dim_set_eq:NN \g_@@_x_final_dim \g_@@_x_initial_dim}
-%    \end{macrocode}
-% If the column is of type |r|, we will draw the dotted line on the right-most abscissa.
+\cs_new_protected:Nn \@@_draw_Vdots:nn
+      {\@@_find_extremities_of_line:nnnn {#1} {#2} 1 0
+       \@@_if_yet_drawn:F
+       {\@@_retrieve_coords:xx {\bool_if:NTF \l_@@_initial_open_bool
+                                  {-medium.north~west}
+                                  {.south~west}} 
+                               {\bool_if:NTF \l_@@_final_open_bool
+                                   {-medium.south~west}
+                                   {.north~west}}
+%    \end{macrocode}
+% The boolean |\l_tmpa_bool| indicates wether the column is of type |l| (|L| of |{NiceArray}|) or may be considered
+% as if.
 %    \begin{macrocode}      
-       \str_if_eq:VnT \l_tmpa_tl {r}
-            {\dim_set:Nn \g_@@_x_initial_dim {\dim_max:nn \g_@@_x_initial_dim \g_@@_x_final_dim}
-             \dim_set_eq:NN \g_@@_x_final_dim \g_@@_x_initial_dim}
-%    \end{macrocode}
-% Now, the coordinates of the line to draw are computed in |\g_@@_x_initial_dim|, |\g_@@_y_initial_dim|,
-% |\g_@@_x_final_dim| and |\g_@@_y_final_dim|. We can draw the line with |\l_@@_draw_tikz_line:| as usual.
+       \bool_set:Nn \l_tmpa_bool 
+                    {\dim_compare_p:nNn \g_@@_x_initial_dim = \g_@@_x_final_dim}
+       \@@_retrieve_coords:xx {\bool_if:NTF \l_@@_initial_open_bool
+                                 {-medium.north}
+                                 {.south}} 
+                              {\bool_if:NTF \l_@@_final_open_bool  
+                                 {-medium.south}
+                                 {.north}}
+%    \end{macrocode}
+% The boolean |\l_tmpb_bool| indicates wether the column is of type |c| (|C| of |{NiceArray}|) or may be considered
+% as if.
 %    \begin{macrocode}      
-       \@@_draw_tikz_line:}
+       \bool_set:Nn \l_tmpb_bool 
+                    {\dim_compare_p:nNn \g_@@_x_initial_dim = \g_@@_x_final_dim}
+       \bool_if:NF \l_tmpb_bool
+            {\dim_gset:Nn \g_@@_x_initial_dim
+                         {\bool_if:NTF \l_tmpa_bool \dim_min:nn \dim_max:nn
+                                       \g_@@_x_initial_dim \g_@@_x_final_dim}
+             \dim_gset_eq:NN \g_@@_x_final_dim \g_@@_x_initial_dim}
+       \@@_draw_tikz_line:}}
 %    \end{macrocode}
 %
 % \interitem
@@ -2402,8 +3117,15 @@ version 2005/12/01 or later.
 % lines. The first diagonal line is drawn and then, all the other diagonal lines are drawn parallel to the first
 % one.
 %    \begin{macrocode}
-\cs_new_protected:Nn \@@_draw_ddots_line:
-   {\@@_retrieve_coords:nn {south~east} {north~west}
+\cs_new_protected:Nn \@@_draw_Ddots:nn
+   {\@@_find_extremities_of_line:nnnn {#1} {#2} 1 1 
+    \@@_if_yet_drawn:F
+    {\@@_retrieve_coords:xx {\bool_if:NTF \l_@@_initial_open_bool
+                                 {-medium.north~west}
+                                 {.south~east}} 
+                            {\bool_if:NTF \l_@@_final_open_bool
+                                 {-medium.south~east}
+                                 {.north~west}}
 %    \end{macrocode}
 % We have retrieved the coordinates in the usual way (they are stored in |\g_@@_x_initial_dim|, etc.).
 % If the parallelization of the diagonals is set, we will have (maybe) to adjust the fourth coordinate.
@@ -2431,24 +3153,31 @@ version 2005/12/01 or later.
 %    \end{macrocode}
 % Now, we can draw the dotted line (after a possible change of |\g_@@_y_initial_dim|).
 %    \begin{macrocode}
-    \@@_draw_tikz_line:}
+    \@@_draw_tikz_line:}}
 %    \end{macrocode}
 %
 % \bigskip
 % We draw the |\Iddots| diagonals in the same way.
 %    \begin{macrocode}
-\cs_new_protected:Nn \@@_draw_iddots_line:
-   {\@@_retrieve_coords:nn {south~west} {north~east} 
-    \bool_if:NT \l_@@_parallelize_diags_bool
-       {\int_incr:N \l_@@_iddots_int
-        \int_compare:nNnTF \l_@@_iddots_int = 1
-          {\dim_set:Nn \l_@@_delta_x_two_dim {\g_@@_x_final_dim - \g_@@_x_initial_dim }
-           \dim_set:Nn \l_@@_delta_y_two_dim {\g_@@_y_final_dim - \g_@@_y_initial_dim }}
-          {\dim_gset:Nn \g_@@_y_final_dim
-                  {\g_@@_y_initial_dim +
-                      (\g_@@_x_final_dim - \g_@@_x_initial_dim)
-                      * \dim_ratio:nn \l_@@_delta_y_two_dim \l_@@_delta_x_two_dim }}}
-    \@@_draw_tikz_line:}
+\cs_new_protected:Nn \@@_draw_Iddots:nn
+   {\@@_find_extremities_of_line:nnnn {#1} {#2} 1 {-1}
+    \@@_if_yet_drawn:F
+    {\@@_retrieve_coords:xx {\bool_if:NTF \l_@@_initial_open_bool
+                              {-medium.north~east}
+                              {.south~west}} 
+                           {\bool_if:NTF \l_@@_final_open_bool
+                              {-medium.south~west}
+                              {.north~east}}
+     \bool_if:NT \l_@@_parallelize_diags_bool
+        {\int_incr:N \l_@@_iddots_int
+         \int_compare:nNnTF \l_@@_iddots_int = 1
+           {\dim_set:Nn \l_@@_delta_x_two_dim {\g_@@_x_final_dim - \g_@@_x_initial_dim}
+            \dim_set:Nn \l_@@_delta_y_two_dim {\g_@@_y_final_dim - \g_@@_y_initial_dim}}
+           {\dim_gset:Nn \g_@@_y_final_dim
+                   {\g_@@_y_initial_dim +
+                       (\g_@@_x_final_dim - \g_@@_x_initial_dim)
+                       * \dim_ratio:nn \l_@@_delta_y_two_dim \l_@@_delta_x_two_dim }}}
+    \@@_draw_tikz_line:}}
 %    \end{macrocode}
 %
 % \bigskip
@@ -2482,30 +3211,57 @@ version 2005/12/01 or later.
 %    \end{macrocode}
 % The integer |\l_tmpa_int| is the number of dots of the dotted line.
 %    \begin{macrocode}
-                     {\int_set:Nn \l_tmpa_int {\dim_ratio:nn {\l_@@_l_dim - 0.54em} 
-                                                             {0.45em}}
+                     {\bool_if:NTF \l_@@_initial_open_bool
+                       {\bool_if:NTF \l_@@_final_open_bool
+                           {\int_set:Nn \l_tmpa_int 
+                                        {\dim_ratio:nn {\l_@@_l_dim} {0.45em}}}
+                           {\int_set:Nn \l_tmpa_int 
+                                        {\dim_ratio:nn {\l_@@_l_dim - 0.3em} {0.45em}}}}
+                       {\bool_if:NTF \l_@@_final_open_bool
+                           {\int_set:Nn \l_tmpa_int 
+                                        {\dim_ratio:nn {\l_@@_l_dim - 0.3em} {0.45em}}}
+                           {\int_set:Nn \l_tmpa_int 
+                                        {\dim_ratio:nn {\l_@@_l_dim - 0.6em} {0.45em}}}}
 %    \end{macrocode}
 % The dimensions |\l_tmpa_dim| and |\l_tmpb_dim| are the coordinates of the vector between two dots in the
 % dotted line.
 %    \begin{macrocode}
-                      \dim_set:Nn \l_tmpa_dim { (\g_@@_x_final_dim - \g_@@_x_initial_dim) 
+                      \dim_set:Nn \l_tmpa_dim {(\g_@@_x_final_dim - \g_@@_x_initial_dim)
                                                  * \dim_ratio:nn {0.45em} \l_@@_l_dim}
-                      \dim_set:Nn \l_tmpb_dim { (\g_@@_y_final_dim - \g_@@_y_initial_dim) 
+                      \dim_set:Nn \l_tmpb_dim {(\g_@@_y_final_dim - \g_@@_y_initial_dim)
                                                  * \dim_ratio:nn {0.45em} \l_@@_l_dim}
 %    \end{macrocode}
+%
+% The length $\ell$ is the length of the dotted line. We note $\Delta$ the length between two dots and $n$ the
+% number of intervals between dots. We note $\delta = \frac12(\ell - n \Delta)$.
+% The distance between the initial extremity of the line and the first dot will be equal to $k\cdot\delta$ where
+% $k=0$, $1$ or $2$. We first compute this number $k$ in |\l_tmpb_int|.
+%    \begin{macrocode}
+                      \int_set:Nn \l_tmpb_int
+                          {\bool_if:NTF \l_@@_initial_open_bool
+                             {\bool_if:NTF \l_@@_final_open_bool 1 0}
+                             {\bool_if:NTF \l_@@_final_open_bool 2 1}}
+%    \end{macrocode}
 % In the loop over the dots (|\int_step_inline:nnnn|), the dimensions |\g_@@_x_initial_dim| and
-% |\g_@@_y_initial_dim| will be used for the coordinates of the dots.
+% |\g_@@_y_initial_dim| will be used for the coordinates of the dots. But, before the loop, we must move until the
+% first dot.
+%
 %    \begin{macrocode}
                       \dim_gadd:Nn \g_@@_x_initial_dim
-                          { (\g_@@_x_final_dim - \g_@@_x_initial_dim)
+                          {  (\g_@@_x_final_dim - \g_@@_x_initial_dim)
                               * \dim_ratio:nn {\l_@@_l_dim - 0.45 em * \l_tmpa_int}
-                                              {\l_@@_l_dim * 2}}
+                                              {\l_@@_l_dim * 2} 
+                              * \l_tmpb_int}
+%    \end{macrocode}
+% (In a multiplication of a dimension and an integer, the integer must always be put in second position.)
+%    \begin{macrocode}         
                       \dim_gadd:Nn \g_@@_y_initial_dim 
-                          { (\g_@@_y_final_dim - \g_@@_y_initial_dim)
+                          {   (\g_@@_y_final_dim - \g_@@_y_initial_dim)
                              * \dim_ratio:nn {\l_@@_l_dim - 0.45 em * \l_tmpa_int}
-                                             {\l_@@_l_dim * 2}}
+                                             {\l_@@_l_dim * 2}
+                             * \l_tmpb_int}
                       \begin{tikzpicture}[overlay]
-                      \int_step_inline:nnn 0 \l_tmpa_int
+                      \int_step_inline:nnnn 0 1 \l_tmpa_int
                          { \pgfpathcircle{\pgfpoint{\g_@@_x_initial_dim}
                                                    {\g_@@_y_initial_dim}}
                                          {0.53pt}
@@ -2544,7 +3300,7 @@ version 2005/12/01 or later.
 % \pkg{nicematrix} rely upon |{NiceArray}|).
 %    \begin{macrocode}
 \NewDocumentCommand \@@_Ldots {s}
-    {\IfBooleanF {#1} {\@@_instruction_of_type:n 0}
+    {\bool_if:nF {#1} {\@@_instruction_of_type:n {Ldots}}
      \bool_if:NF \l_@@_nullify_dots_bool {\phantom \@@_ldots}
      \@@_add_to_empty_cells:}
 %    \end{macrocode}
@@ -2552,7 +3308,7 @@ version 2005/12/01 or later.
 % \bigskip
 %    \begin{macrocode}
 \NewDocumentCommand \@@_Cdots {s}
-    {\IfBooleanF {#1} {\@@_instruction_of_type:n 1}
+    {\bool_if:nF {#1} {\@@_instruction_of_type:n {Cdots}}
      \bool_if:NF \l_@@_nullify_dots_bool {\phantom \@@_cdots}
      \@@_add_to_empty_cells:}
 %    \end{macrocode}
@@ -2560,7 +3316,7 @@ version 2005/12/01 or later.
 % \bigskip
 %    \begin{macrocode}
 \NewDocumentCommand \@@_Vdots {s}
-    {\IfBooleanF {#1} {\@@_instruction_of_type:n 2}
+    {\bool_if:nF {#1} {\@@_instruction_of_type:n {Vdots}}
      \bool_if:NF \l_@@_nullify_dots_bool {\phantom \@@_vdots}
      \@@_add_to_empty_cells:}
 %    \end{macrocode}
@@ -2568,7 +3324,7 @@ version 2005/12/01 or later.
 % \bigskip
 %    \begin{macrocode}
 \NewDocumentCommand \@@_Ddots {s}
-    {\IfBooleanF {#1} {\@@_instruction_of_type:n 3}
+    {\bool_if:nF {#1} {\@@_instruction_of_type:n {Ddots}}
      \bool_if:NF \l_@@_nullify_dots_bool {\phantom \@@_ddots}
      \@@_add_to_empty_cells:}
 %    \end{macrocode}
@@ -2576,7 +3332,7 @@ version 2005/12/01 or later.
 % \bigskip
 %    \begin{macrocode}
 \NewDocumentCommand \@@_Iddots {s}
-    {\IfBooleanF {#1} {\@@_instruction_of_type:n 4}
+    {\bool_if:nF {#1} {\@@_instruction_of_type:n {Iddots}}
      \bool_if:NF \l_@@_nullify_dots_bool {\phantom \@@_iddots}
      \@@_add_to_empty_cells:}
 %    \end{macrocode}
@@ -2590,47 +3346,73 @@ version 2005/12/01 or later.
    \hspace}
 %    \end{macrocode}
 %
+%
 % \bigskip
-% The command |\@@_NiceMatrixEndPoint:| will be linked to |\NiceMatrixEndPoint| in |{NiceArray}|.
+% In the environment |{NiceArray}|, the command |\multicolumn| will be linked to the following command
+% |\@@_multicolumn:nnn|.
 %    \begin{macrocode}
-\cs_new_protected:Nn \@@_NiceMatrixEndPoint:
-     {\kern 0.5pt}
+\cs_set_eq:NN \@@_old_multicolumn \multicolumn
+\cs_new:Nn \@@_multicolumn:nnn
+       {\@@_old_multicolumn{#1}{#2}{#3}
+        \int_compare:nNnT #1 > 1
+            {\seq_gput_left:Nx \g_@@_multicolumn_cells_seq
+                               {\int_eval:n {\g_@@_row_int} - 
+                                \int_use:N \g_@@_column_int}
+             \seq_gput_left:Nn \g_@@_multicolumn_sizes_seq {#1}}
+        \int_gadd:Nn \g_@@_column_int {#1-1}}
 %    \end{macrocode}
 %
+%
 % \bigskip
-% The command |\@@_Hdotsfor| will be linked to |\Hdotsfor| in |{NiceArray}|. This command uses an optionnal
+% The command |\@@_Hdotsfor| will be linked to |\Hdotsfor| in |{NiceArray}|. This command uses an optional
 % argument like |\hdotsfor| but this argument is discarded (in |\hdotsfor|, this argument is used for fine tuning
 % of the space beetween two consecutive dots). 
+% Tikz nodes are created for all the cells of the array, even the implicit cells of the |\Hdotsfor|.
 %    \begin{macrocode}
-\NewDocumentCommand \@@_Hdotsfor {O{} m}
+\NewDocumentCommand {\@@_Hdotsfor} {O{} m}
+     {\tl_gput_right:Nx \g_@@_lines_to_draw_tl 
+           {\exp_not:N \@@_draw_Hdotsfor:nnn
+                       {\int_use:N \g_@@_row_int} 
+                       {\int_use:N \g_@@_column_int}
+                       {#2}}
+      \prg_replicate:nn {#2-1} {&}}
 %    \end{macrocode}
-% First, we store in the |code-after| (that is in |\g_@@_code_after_tl|) a command |\line| to draw the dotted line
-% after the construction of the matrix.
+% 
+% \medskip
 %    \begin{macrocode}
-               {\int_set:Nn \l_tmpa_int {\g_@@_column_int - 1}
-                \int_set:Nn \l_tmpb_int {\g_@@_column_int + #2}
-                \tl_gput_right:Nx \g_@@_code_after_tl
-                       {\exp_not:N \line {\int_use:N\g_@@_row_int-\int_use:N\l_tmpa_int}
-                                         {\int_use:N\g_@@_row_int-\int_use:N\l_tmpb_int}}
+\cs_new_protected:Nn \@@_draw_Hdotsfor:nnn
+       {\bool_set_false:N \l_@@_initial_open_bool
+        \bool_set_false:N \l_@@_final_open_bool
 %    \end{macrocode}
-% Then, we insert the correct number of ampersands (|&|).
+% For the row, it's easy.
 %    \begin{macrocode}
-                \prg_replicate:nn {#2-1} {&}}
+        \int_set:Nn \l_@@_initial_i_int {#1}
+        \int_set:Nn \l_@@_final_i_int {#1}
 %    \end{macrocode}
-% Tikz nodes are created for all the cells of the array, even the implicit cells of the |\Hdotsfor|.
-%
-% \subsection{We process the options}
-%
-% We process the options when the package is loaded (with |\usepackage|) but we recommend to use
-% |\NiceMatrixOptions| instead. 
-%
-% We must process these options after the definition of the environment |{NiceMatrix}| because the option
-% |renew-matrix| execute the code |\cs_set_eq:NN \env@matrix \NiceMatrix|. 
-%
-% Of course, the command |\NiceMatrix| must be defined before such an instruction is executed.
+% For the column, it's a bit more complicated.
 %    \begin{macrocode}
-\ProcessKeysOptions {NiceMatrix}
+        \int_compare:nNnTF #2 = 1
+              {\int_set:Nn \l_@@_initial_j_int 1
+               \bool_set_true:N \l_@@_initial_open_bool}
+              {\int_set:Nn \l_tmpa_int {#2-1}
+               \@@_if_not_empty_cell:nnTF \l_@@_initial_i_int \l_tmpa_int
+                 {\int_set:Nn \l_@@_initial_j_int {#2-1}}
+                 {\int_set:Nn \l_@@_initial_j_int {#2}
+                  \bool_set_true:N \l_@@_initial_open_bool}}
+        \int_compare:nNnTF {#2+#3-1} = \g_@@_column_int
+              {\int_set:Nn \l_@@_final_j_int {#2+#3-1}
+               \bool_set_true:N \l_@@_final_open_bool}
+              {\int_set:Nn \l_tmpa_int {#2+#3}
+               \@@_if_not_empty_cell:nnTF \l_@@_final_i_int \l_tmpa_int
+                 {\int_set:Nn \l_@@_final_j_int {#2+#3}}
+                 {\int_set:Nn \l_@@_final_j_int {#2+#3-1}
+                  \bool_set_true:N \l_@@_final_open_bool}}
+        \bool_if:nT {\l_@@_initial_open_bool || \l_@@_final_open_bool}
+                    \@@_create_extra_nodes: 
+        \@@_actually_draw_Ldots:}
 %    \end{macrocode}
+% 
+%
 %
 % \subsection{The command \textbackslash line accessible in code-after}
 %
@@ -2657,54 +3439,7 @@ version 2005/12/01 or later.
 % The commands |\Ldots|, |\Cdots|, |\Vdots|, |\Ddots|, |\Iddots| don't use this command because they have to do
 % other settings (for example, the diagonal lines must be parallelized).
 %
-% \subsection{The error messages}
-%    \begin{macrocode}
-\msg_new:nnnn {nicematrix}
-              {Impossible~instruction}
-              {It's~not~possible~to~execute~the~instruction~
-               \int_case:nn \l_@@_type_int
-                 {0 {\token_to_str:N \Ldots}
-                  1 {\token_to_str:N \Cdots}
-                  2 {\token_to_str:N \Vdots}
-                  3 {\token_to_str:N \Ddots}}~in~the~row~\int_use:N\l_@@_row_int\ 
-               ~and~the~column~\int_use:N\l_@@_column_int\space of~the~matrix~
-               because~it's~impossible~to~find~one~of~its~extremities~  
-               (both~extremities~must~be~non~empty~cells~of~the~matrix).~
-               If~you~go~on,~the~instruction~will~be~ignored.}
-              {You~can~specify~an~end~of~line~on~a~empty~cell~
-               with~\token_to_str:N \NiceMatrixEndPoint.}
-%    \end{macrocode}
-%
-%    \begin{macrocode}
-\msg_new:nnn {nicematrix}
-             {Multicolumn~forbidden}
-             {The~command~\token_to_str:N \multicolumn\ 
-              is~forbidden~in~the~environment~\{\@currenvir\}~ 
-              and~its~variants.~The~command~\token_to_str:N \hdotsfor\ 
-              of~amsmath~is~also~forbidden~since~it~uses~
-              \token_to_str:N \multicolumn\ ~(but~you~can~use~\token_to_str:N \Hdotsfor\ 
-              ~instead).~You~can~go~on~but~your~matrix~may~be~wrong.}
-%    \end{macrocode}
-% 
-%    \begin{macrocode}
-\msg_new:nnn {nicematrix} 
-             {We~are~yet~in~an~environment~NiceArray}
-             {Environments~\{NiceArray\}~(or~\{NiceMatrix\},~etc.)~can't~be~
-              nested.~We~can~go~on,~but,~maybe,~you~will~have~errors~or~an~incorrect~
-              result.}
-%    \end{macrocode}
 %
-%    \begin{macrocode}
-\msg_new:nnnn {nicematrix}
-              {Duplicate~name}
-              {The~name~"#1"~is~already~used~and~you~shouldn't~use~
-               the~same~environment~name~twice.~You~can~go~on,~but,~
-               maybe,~you~will~have~incorrect~results~especially~ 
-               if~you~use~"columns-width=auto".\\
-               For~a~list~of~the~names~already~used,~type~H~<return>.}
-              {The~names~already~defined~in~this~document~are:~
-               \seq_use:Nnnn~\g_@@_names_seq~{,~} {,~} {~and~}.}
-%    \end{macrocode}
 %
 % \subsection{The environment \{NiceMatrixBlock\}}
 %
@@ -2718,9 +3453,10 @@ version 2005/12/01 or later.
 % As of now, there is only one option available for the environment |{NiceMatrixBlock}|.
 %    \begin{macrocode}
 \keys_define:nn {NiceMatrix/NiceMatrixBlock} 
-      {auto-columns-width .code:n = {\bool_set_true:N \l_@@_block_auto_columns_width_bool
-                                     \dim_gzero_new:N \g_@@_max_cell_width_dim
-                                     \bool_set_true:N \l_@@_auto_columns_width_bool}}
+      {auto-columns-width .code:n = 
+                           {\bool_set_true:N \l_@@_block_auto_columns_width_bool
+                            \dim_gzero_new:N \g_@@_max_cell_width_dim
+                            \bool_set_true:N \l_@@_auto_columns_width_bool}}
 %    \end{macrocode}
 %
 % \bigskip
@@ -2738,9 +3474,9 @@ version 2005/12/01 or later.
 %    \begin{macrocode}
     {\bool_if:NT \l_@@_block_auto_columns_width_bool
           {\iow_now:Nn \@mainaux {\ExplSyntaxOn}
-           \int_step_inline:nnn \l_@@_first_env_block_int \g_@@_env_int
+           \int_step_inline:nnnn \l_@@_first_env_block_int 1 \g_@@_env_int
                {\iow_now:Nx \@mainaux         
-                   {\cs_gset:cpn {_@@_max_cell_width_##1} 
+                   {\cs_gset:cpn {@@_max_cell_width_##1} 
                                  {\dim_use:N \g_@@_max_cell_width_dim}}}
            \iow_now:Nn \@mainaux {\ExplSyntaxOff}}}
 %    \end{macrocode}
@@ -2769,16 +3505,22 @@ version 2005/12/01 or later.
                                             {\dim_set:Nn \l_@@_columns_width_dim {#1}},
       columns-width     .value_required:n = true,
       name              .code:n           = {\seq_if_in:NnTF \g_@@_names_seq {#1}
-                                                {\msg_error:nnn {nicematrix}
-                                                                {Duplicate~name}
-                                                                {#1}}
+                                                {\@@_msg_error:nn {Duplicate~name} {#1}}
                                                 {\seq_gput_left:Nn \g_@@_names_seq {#1}}
-                                             \tl_gset:Nn \g_@@_name_tl {#1}},
+                                             \tl_set:Nn \l_@@_name_tl {#1}},
       name              .value_required:n = true,
-      code-after        .tl_gset:N         = \g_@@_code_after_tl,
-      code-after        .initial:n    = \c_empty_tl,
+      code-after        .tl_set:N          = \l_@@_code_after_tl,
+      code-after        .initial:n         = \c_empty_tl,
       code-after        .value_required:n = true,
-      unknown .code:n  = \msg_error:nn {nicematrix} {Unknown~option~for~NiceArrayC}}
+      create-extra-nodes  .bool_set:N   = \l_@@_extra_nodes_bool,
+      create-extra-nodes  .default:n    = true,
+      left-margin  .dim_set:N  = \l_@@_left_margin_dim,
+      left-margin  .default:n  = \arraycolsep,
+      right-margin .dim_set:N  = \l_@@_right_margin_dim,
+      right-margin .default:n  = \arraycolsep,
+      extra-left-margin  .dim_set:N  = \l_@@_extra_left_margin_dim,
+      extra-right-margin .dim_set:N  = \l_@@_extra_right_margin_dim,
+      unknown .code:n  = \@@_msg_error:n {Unknown~option~for~NiceArrayC}}
 %    \end{macrocode}
 %
 %    \begin{macrocode}
@@ -2792,10 +3534,15 @@ version 2005/12/01 or later.
                code-after,~
                code-for-last-col,~
                columns-width,~
+               create-extra-nodes,~
+               extra-left-margin,~
+               extra-right-margin,~
+               left-margin,~
                name,~
                nullify-dots,~
                parallelize-diags~
-               and~renew-dots.}
+               renew-dots~
+               and~right-margin.}
 %    \end{macrocode}
 %
 % \bigskip
@@ -2809,7 +3556,7 @@ version 2005/12/01 or later.
 % |{NiceArrayRCwithDelims}|.
 %    \begin{macrocode}
 \cs_new_protected:Nn \@@_NiceArrayC:n
-    {
+    {\bool_set_true:N \l_@@_exterior_column_bool
      \begin{NiceArray}
 %    \end{macrocode}
 % The beginning of the preamble is the argument of the environment |{pNiceArrayC}|. 
@@ -2822,21 +3569,18 @@ version 2005/12/01 or later.
 % |\hbox_set:Nw \l_tmpa_box| ... |\hbox_set_end:|.
 %    \begin{macrocode}
                 >{\int_gincr:N \g_@@_column_int
+                 \int_gset:Nn \g_@@_column_total_int 
+                              {\int_max:nn \g_@@_column_total_int \g_@@_column_int}
                   \hbox_set:Nw \l_tmpa_box
-                  \tl_if_empty:NTF \g_@@_name_tl
-                   {\tikz[remember~picture, inner~sep = 0pt, minimum~width = 0pt, baseline]
-                       \node [anchor=base,
-                              name = nm-\int_use:N \g_@@_env_int-
-                                        \int_use:N \g_@@_row_int-
-                                        \int_use:N \g_@@_column_int] }
-                   {\tikz[remember~picture, inner~sep = 0pt, minimum~width = 0pt, baseline]
+                    \tikz[remember~picture, inner~sep=0pt, minimum~width=0pt, baseline]
                        \node [anchor=base,
                               name = nm-\int_use:N \g_@@_env_int-
                                         \int_use:N \g_@@_row_int-
                                         \int_use:N \g_@@_column_int,
-                              alias = \g_@@_name_tl-
-                                      \int_use:N \g_@@_row_int-
-                                      \int_use:N \g_@@_column_int] }
+                              alias = \tl_if_empty:NF \l_@@_name_tl
+                                      {\l_@@_name_tl-
+                                       \int_use:N \g_@@_row_int-
+                                       \int_use:N \g_@@_column_int}] 
                      \bgroup $ % $ 
                      \l_@@_code_for_last_col_tl
                  }
@@ -2852,25 +3596,24 @@ version 2005/12/01 or later.
                   \dim_gset:Nn \g_@@_width_last_col_dim
                      {\dim_max:nn \g_@@_width_last_col_dim
                                   {\box_wd:N \l_tmpa_box}}
-                  \tl_gput_right:Nn \g_@@_preamble_aux_tl {#1}
                   \skip_horizontal:n {-2\arraycolsep}
 %    \end{macrocode}
 % The content of the cell is inserted in an overlapping position.
 %    \begin{macrocode}
                   \hbox_overlap_right:n 
-                       {\skip_horizontal:n {2\arraycolsep}
+                       {\skip_horizontal:n 
+                               { 2\arraycolsep + \l_@@_right_margin_dim 
+                                               + \l_@@_extra_right_margin_dim}
                         \box_use:N \l_tmpa_box}}}}
 %    \end{macrocode}
 % This ends the preamble of the array that will be constructed (a rather long preamble, indeed).
 %
 % \bigskip
-% All the environments of the type of |{pNiceArrayC}| will be constructed over |{NiceArrayCwithDelims}|. The first
+% The environments of the type of |{pNiceArrayC}| will be constructed over |{NiceArrayCwithDelims}|. The first
 % two arguments of this environment are the left and the right delimiter.
 %    \begin{macrocode}
 \NewDocumentEnvironment{NiceArrayCwithDelims} {mm O{} m O{}}
-    {\bool_set_false:N \l_@@_direct_NiceArray_bool
-     \tl_gclear:N \g_@@_code_after_tl
-     \dim_gzero_new:N \g_@@_width_last_col_dim
+    {\dim_gzero_new:N \g_@@_width_last_col_dim
      \keys_set:nn {NiceMatrix/NiceArrayC} {#3,#5}
      \bool_set_false:N \l_@@_exterior_arraycolsep_bool
      \tl_set:Nn \l_@@_pos_env_tl c
@@ -2921,64 +3664,6 @@ version 2005/12/01 or later.
 %
 % The code in this section can be removed without affecting the previous code.
 % 
-% \medskip
-%
-% If the environment is used with the option |columns-width=auto|, the construction 
-%
-% \begin{Verbatim}
-% \begin{pNiceArrayRC}{~slshape#preamble@}[columns-width=auto]
-%  ~slshape#first row@ \\
-%  ~slshape#second row@ \\
-%  ~slshape#third row@ \\
-%  ~slshape#etc.@ \\
-% \end{pNiceArrayRC}
-% \end{Verbatim}
-% 
-% is transformed in the following construction :
-% 
-% \begin{Verbatim}
-% \begin{NiceMatrixBlock}[auto-columns-width]
-% \vbox{\hbox{\hphantom{~slshape#an open parenthesis@}
-%             $\begin{NiceArray}{~slshape#preamble@}
-%               ~slshape#first row@ \\
-%              \end{NiceArray}$}
-%       \hbox{$\begin{pNiceArrayC}{~slshape#preamble@}
-%               ~slshape#second row@ \\
-%               ~slshape#third row@ \\
-%               ~slshape#etc.@ \\
-%              \end{pNiceArrayC}$}}
-% \end{NiceMatrixBlock}
-% \end{Verbatim}
-% 
-%
-% \bigskip
-% If the environment is used with a numerical value for the option |columns-width|, the construction 
-%
-% \begin{Verbatim}
-% \begin{pNiceArrayRC}{~slshape#preamble@}[columns-width=~slshape#value@]
-%  ~slshape#first row@ \\
-%  ~slshape#second row@ \\
-%  ~slshape#third row@ \\
-%  ~slshape#etc.@ \\
-% \end{pNiceArrayRC}
-% \end{Verbatim}
-% 
-% is transformed in the following contruction :
-% 
-% \begin{Verbatim}
-% \NiceMatrixOptions{columns-width=~slshape#value@}
-% \vbox{\hbox{~slshape#skip of the width of a parenthesis@
-%             $\begin{NiceArray}{~slshape#preamble@}
-%               ~slshape#first row@ \\
-%              \end{NiceArray}$}
-%       \hbox{$\begin{pNiceArrayC}{~slshape#preamble@}
-%               ~slshape#second row@ \\
-%               ~slshape#third row@ \\
-%               ~slshape#etc.@ \\
-%              \end{pNiceArrayC}$}}
-% \end{Verbatim}
-% 
-% (in the group created by the environment).
 %
 % \bigskip
 %    \begin{macrocode}
@@ -2992,15 +3677,25 @@ version 2005/12/01 or later.
    code-for-first-row   .tl_set:N   = \l_@@_code_for_first_row_tl,
    code-for-last-col    .tl_set:N   = \l_@@_code_for_last_col_tl,
    code-for-last-col    .value_required:n = true,
-   columns-width        .tl_set:N   = \l_@@_columns_width_tl,
+   columns-width        .code:n     = \str_if_eq:nnTF {#1} {auto}
+                                         {\bool_set_true:N 
+                                                \l_@@_auto_columns_width_bool}
+                                         {\dim_set:Nn \l_@@_columns_width_dim {#1}},
+   columns-width        .value_required:n = true,
    name                 .code:n     = {\seq_if_in:NnTF \g_@@_names_seq {#1}
-                                          {\msg_error:nnn {nicematrix}
-                                                          {Duplicate~name}
-                                                          {#1}}
+                                          {\@@_msg_error:nn {Duplicate~name} {#1}}
                                           {\seq_gput_left:Nn \g_@@_names_seq {#1}}
-                                       \tl_gset:Nn \l_@@_name_tl {#1}},
-   code-after           .tl_set:N   = \l_@@_code_after_tl,
-   unknown .code:n  = \msg_error:nn {nicematrix} {Unknown~option~for~NiceArrayRC}}
+                                       \tl_set:Nn \l_@@_name_tl {#1}},
+   code-after           .tl_set:N    = \l_@@_code_after_tl,
+   create-extra-nodes   .bool_set:N  = \l_@@_extra_nodes_bool,
+   create-extra-nodes   .default:n   = true,
+   left-margin  .dim_set:N  = \l_@@_left_margin_dim,
+   left-margin  .default:n  = \arraycolsep,
+   right-margin .dim_set:N  = \l_@@_right_margin_dim,
+   right-margin .default:n  = \arraycolsep,
+   extra-left-margin  .dim_set:N  = \l_@@_extra_left_margin_dim,
+   extra-right-margin .dim_set:N  = \l_@@_extra_right_margin_dim,
+   unknown .code:n  = \@@_msg_error:n {Unknown~option~for~NiceArrayRC}}
 %    \end{macrocode}
 %
 %    \begin{macrocode}
@@ -3014,83 +3709,55 @@ version 2005/12/01 or later.
                code-after,~
                code-for-last-col,~
                code-for-first-row,~
-               columns-width~(in~fact~mandatory),~
+               columns-width,~
+               create-extra-nodes,~
+               extra-left-margin,~
+               extra-right-margin,~
+               left~margin,~
                name,~
                nullify-dots,~
-               parallelize-diags~
-               and~renew-dots.}
+               parallelize-diags,~
+               renew-dots~
+               and~right~margin.}
 %    \end{macrocode}
 %
-%    \begin{macrocode}
-\msg_new:nnn {nicematrix}
-             {The~key~columns-width~is~mandatory}
-             {In~the~environment~\{\@currenvir\}~you~must~use~the~
-              key~"columns-width"~either~with~a~numerical~value~
-              or~the~special~value~"auto".\\
-              If~you~go~on,~the~value~"auto"~will~be~used~for~
-              "columns-width".}
-%    \end{macrocode}
 %
 % The first and the second argument of the environment |{NiceArrayRCwithDelims}| are the delimiters which will be
 % used in the array. Usually, the final user will not use directly this environment |{NiceArrayRCwithDelims}|
 % because he will use one of the variants |{pNiceArrayRC}|, |{vNiceArrayRC}|, etc.
+%
 %    \begin{macrocode}
-\NewDocumentEnvironment{NiceArrayRCwithDelims} {mm O{} m O{}}
-    {\tl_clear_new:N \l_@@_columns_width_tl
-     \tl_clear_new:N \l_@@_name_tl
-     \tl_clear_new:N \l_@@_code_after_tl
-     \keys_set:nn {NiceMatrix/NiceArrayRC} {#3,#5} 
-     \tl_gset_eq:NN \g_@@_name_tl \l_@@_name_tl
-     \tl_if_empty:NT \l_@@_columns_width_tl
-             {\msg_error:nn {nicematrix} {The~key~columns-width~is~mandatory}
-              \tl_set:Nn \l_@@_columns_width_tl {auto}}
-     \str_if_eq:nVTF {auto} \l_@@_columns_width_tl 
-        {\begin{NiceMatrixBlock}[auto-columns-width]}
-        {\NiceMatrixOptions{columns-width = \l_@@_columns_width_tl} }
-     \vbox\bgroup\hbox\bgroup
-%    \end{macrocode}
-% Here, it would be possible to use a |\hphantom| but we prefer to use \pkg{expl3} instructions.
-%    \begin{macrocode}
-     \hbox_set:Nn \l_tmpa_box {$\left#1\vbox_to_ht:nn{2cm}{}\right.$}
-     \skip_horizontal:n {\box_wd:N \l_tmpa_box - \nulldelimiterspace}
-%    \end{macrocode}
-% We give the value $-1$ to |\l_@@_number_of_first_row_int| and, therefore, the first row of the array will have
-% the number $0$ (the final user will use this value when using, for example, the command |\line| in |code-after|).
-%    \begin{macrocode}
-     \int_set:Nn \l_@@_number_of_first_row_int {-1}
-     \tl_set_eq:NN \l_@@_code_for_cell_tl \l_@@_code_for_first_row_tl
-%    \end{macrocode}
-% We read staticly the first row of the array given by the user because we will use the first row to
-% construct an environment |{NiceArray}|. \emph{We read until the first control sequence} |\\|. Therefore, it's not 
-% possible to use a sub-array with this control sequence in the first row of the array.
-%    \begin{macrocode}
-     \cs_set:Npn \@@_replace_first_line ##1\\{
-           $\begin{NiceArray}{*\c@MaxMatrixCols{C}}
-             ##1
-            \end{NiceArray}$
-           \egroup \hbox\bgroup 
-%    \end{macrocode}
-% We decrement the number of the environment because we want the same number for both constructed environments.
-%    \begin{macrocode}
-           \int_gdecr:N \g_@@_env_int
-           \tl_gset_eq:NN \g_@@_name_tl \l_@@_name_tl
-           \tl_gset_eq:NN \g_@@_code_after_tl \l_@@_code_after_tl
-           \bool_set_false:N \l_@@_direct_NiceArray_bool
-           \dim_gzero_new:N \g_@@_width_last_col_dim
-           \bool_set_false:N \l_@@_exterior_arraycolsep_bool
-           \tl_set:Nn \l_@@_pos_env_tl c
-           $\left#1 % $
+\NewDocumentEnvironment {NiceArrayRCwithDelims} {mm O{} m O{}}
+    {\int_zero:N \l_@@_nb_first_row_int 
+     \dim_gzero_new:N \g_@@_width_last_col_dim
+     \keys_set:nn {NiceMatrix/NiceArrayRC} {#3,#5}
+     \bool_set_false:N \l_@@_exterior_arraycolsep_bool
+     \tl_set:Nn \l_@@_pos_env_tl c
+     \box_clear_new:N \l_@@_the_array_box
+     \hbox_set:Nw \l_@@_the_array_box
+           $ % $
            \@@_NiceArrayC:n {#4}}
-     \@@_replace_first_line 
+    {      \end{NiceArray}
+           $ % $
+     \hbox_set_end:
+     \dim_set:Nn \l_tmpa_dim
+            { ( \dim_max:nn {12pt} 
+                            {\g_@@_max_ht_row_one_dim + \g_@@_max_dp_row_zero_dim})
+              + \g_@@_max_ht_row_zero_dim 
+              - \g_@@_max_ht_row_one_dim }
+     \hbox_set:Nn \l_tmpa_box
+        {$ % $
+         \left#1
+         \vcenter {\skip_vertical:n {- \l_tmpa_dim}
+                   \box_use_drop:N \l_@@_the_array_box}
+         \right#2
+         $ % $
+         \skip_horizontal:n \g_@@_width_last_col_dim}
+     \box_set_ht:Nn \l_tmpa_box {\box_ht:N \l_tmpa_box + \l_tmpa_dim}
+     \box_use_drop:N \l_tmpa_box
     }
-    {\end{NiceArray}
-     \right#2$ % $
-     \skip_horizontal:n \g_@@_width_last_col_dim
-     \egroup\egroup
-     \str_if_eq:nVT {auto} \l_@@_columns_width_tl 
-        {\end{NiceMatrixBlock}} }
 %    \end{macrocode}
-%
+% 
 % \bigskip
 % In the following environments, we don't use the form with |\begin{...}| and |\end{...}| because we use
 % |\@currenvir| in the error message for an unknown option.
@@ -3125,13 +3792,256 @@ version 2005/12/01 or later.
 %    \end{macrocode}
 %
 %
+% \subsection{The extra nodes}
+%
+% First, two variants of the functions |\dim_min:nn| and |\dim_max:nn|.
+%    \begin{macrocode}
+\cs_generate_variant:Nn \dim_min:nn {vn}
+\cs_generate_variant:Nn \dim_max:nn {vn}
+%    \end{macrocode}
+%
+%
+%
+% \bigskip
+% For each row $i$, we compute two dimensions \texttt{l_@@_row_\textsl{i}_min_dim} and
+% \texttt{l_@@_row_\textsl{i}_max_dim}. The dimension \texttt{l_@@_row_\textsl{i}_min_dim} is the minimal
+% $y$-value of all the cells of the row~$i$. The dimension \texttt{l_@@_row_\textsl{i}_max_dim} is the maximal
+% $y$-value of all the cells of the row~$i$.
+%
+% Similarly, for each column $j$, we compute two dimensions \texttt{l_@@_column_\textsl{j}_min_dim} and
+% \texttt{l_@@_column_\textsl{j}_max_dim}. The dimension \texttt{l_@@_column_\textsl{j}_min_dim} is the minimal
+% $x$-value of all the cells of the column~$j$. The dimension \texttt{l_@@_column_\textsl{j}_max_dim} is the maximal
+% $x$-value of all the cells of the column~$j$.
+%
+% Since these dimensions will be computed as maximum or minimum, we initialize them to |\c_max_dim| or |-\c_max_dim|.
+%    \begin{macrocode}
+\cs_new_protected:Nn \@@_create_extra_nodes:
+     {\begin{tikzpicture}[remember~picture,overlay]
+      \int_step_variable:nnnNn \l_@@_nb_first_row_int 1 \g_@@_row_int \@@_i
+          {\dim_zero_new:c {l_@@_row_\@@_i _min_dim} 
+           \dim_set_eq:cN {l_@@_row_\@@_i _min_dim} \c_max_dim
+           \dim_zero_new:c {l_@@_row_\@@_i _max_dim} 
+           \dim_set:cn {l_@@_row_\@@_i _max_dim} {-\c_max_dim}}
+      \int_step_variable:nnnNn 1 1 \g_@@_column_total_int \@@_j
+          {\dim_zero_new:c {l_@@_column_\@@_j _min_dim} 
+           \dim_set_eq:cN {l_@@_column_\@@_j _min_dim} \c_max_dim
+           \dim_zero_new:c {l_@@_column_\@@_j _max_dim} 
+           \dim_set:cn {l_@@_column_\@@_j _max_dim} {-\c_max_dim}}
+%    \end{macrocode}
+% We begin the two nested loops over the rows and the columns of the array.
+%    \begin{macrocode}
+      \int_step_variable:nnnNn \l_@@_nb_first_row_int 1 \g_@@_row_int \@@_i
+          {\int_step_variable:nnnNn 1 1 \g_@@_column_total_int \@@_j
+%    \end{macrocode}
+% Maybe the cell ($i$-$j$) is an implicit cell (that is to say a cell after implicit ampersands |&|). In this case,
+% of course, we don't update the dimensions we want to compute.
+%    \begin{macrocode}
+            {\cs_if_exist:cT {pgf@sh@ns@nm-\int_use:N \g_@@_env_int-\@@_i-\@@_j}
+%    \end{macrocode}
+% We retrieve the coordinates of the anchor |south west| of the (normal) node of the cell ($i$-$j$). They will be
+% stored in |\pgf@x| and |\pgf@y|.
+%    \begin{macrocode}
+               {\tikz@parse@node \pgfutil@firstofone 
+                           (nm-\int_use:N \g_@@_env_int-\@@_i-\@@_j.south~west)
+                \dim_set:cn {l_@@_row_\@@_i _min_dim}
+                            {\dim_min:vn {l_@@_row_\@@_i _min_dim} \pgf@y}
+                \seq_if_in:NxF \g_@@_multicolumn_cells_seq {\@@_i-\@@_j}
+                   {\dim_set:cn {l_@@_column_\@@_j _min_dim}
+                               {\dim_min:vn {l_@@_column_\@@_j _min_dim} \pgf@x}}
+%    \end{macrocode}
+% We retrieve the coordinates of the anchor |north east| of the (normal) node of the cell ($i$-$j$). They will be
+% stored in |\pgf@x| and |\pgf@y|.
+%    \begin{macrocode}
+                \tikz@parse@node \pgfutil@firstofone 
+                           (nm-\int_use:N \g_@@_env_int-\@@_i-\@@_j.north~east)
+                \dim_set:cn {l_@@_row_\@@_i _max_dim}
+                            {\dim_max:vn {l_@@_row_\@@_i _max_dim} \pgf@y}
+                \seq_if_in:NxF \g_@@_multicolumn_cells_seq {\@@_i-\@@_j}
+                   {\dim_set:cn {l_@@_column_\@@_j _max_dim}
+                               {\dim_max:vn {l_@@_column_\@@_j _max_dim} \pgf@x}}}
+          }}
+%    \end{macrocode}
+% Now, we can create the ``medium nodes''. We use a command |\@@_create_nodes:| because this command will also be used
+% for the creation of the ``large nodes'' (after changing the value of |name-suffix|).
+%    \begin{macrocode} 
+      \tikzset{name~suffix = -medium}
+      \@@_create_nodes:
+%    \end{macrocode}
+% 
+% \bigskip
+% For ``large nodes'', the eventual ``first row'' and ``last column'' (in environments like |{pNiceArrayRC}|) don't
+% interfer. That's why the loop over the rows will start at 1 and the loop over the columns will stop at
+% $|\g_@@_column_int|$ (and not |\g_@@_column_total_int|).\footnote{We recall that |\g_@@_column_total_int| is
+% equal to |\g_@@_column_int| except if there is an exterior column. In this case, |\g_@@_column_total_int| is equal
+% to |\g_@@_column_int|${}+1$.}
+%     \begin{macrocode}
+      \int_set:Nn \l_@@_nb_first_row_int 1
+%    \end{macrocode}
+% We have to change the values of all the dimensions \texttt{l_@@_row_\textsl{i}_min_dim},
+% \texttt{l_@@_row_\textsl{i}_max_dim}, \texttt{l_@@_column_\textsl{j}_min_dim} and
+% \texttt{l_@@_column_\textsl{j}_max_dim}. 
+%    \begin{macrocode} 
+      \int_step_variable:nnnNn 1 1 {\g_@@_row_int-1} \@@_i
+         {\dim_set:cn {l_@@_row_\@@_i _min_dim}  
+                      {(  \dim_use:c {l_@@_row_\@@_i _min_dim} 
+                        + \dim_use:c {l_@@_row_\int_eval:n{\@@_i+1}_max_dim}) / 2}
+          \dim_set_eq:cc {l_@@_row_\int_eval:n{\@@_i+1}_max_dim} 
+                         {l_@@_row_\@@_i _min_dim} }
+      \int_step_variable:nnnNn 1 1 {\g_@@_column_int-1} \@@_j
+         {\dim_set:cn {l_@@_column_\@@_j _max_dim}  
+                      {(  \dim_use:c {l_@@_column_\@@_j _max_dim} 
+                        + \dim_use:c {l_@@_column_\int_eval:n{\@@_j+1}_min_dim}) / 2}
+          \dim_set_eq:cc {l_@@_column_\int_eval:n{\@@_j+1}_min_dim} 
+                         {l_@@_column_\@@_j _max_dim} }
+      \dim_sub:cn {l_@@_column_1_min_dim} \g_@@_left_margin_dim
+      \dim_add:cn {l_@@_column_\int_use:N \g_@@_column_int _max_dim} 
+                  \g_@@_right_margin_dim
+%    \end{macrocode}
+% Now, we can actually create the ``large nodes''.
+%    \begin{macrocode}
+      \tikzset{name~suffix = -large}
+      \@@_create_nodes:
+      \end{tikzpicture}
+%    \end{macrocode}
+%
+% \medskip
+% When used once, the command |\@@_create_extra_nodes:| must become no-op (in the current TeX group). That's why we
+% put a nullification of the command.
+%    \begin{macrocode}
+      \cs_set:Nn \@@_create_extra_nodes: {}}
+%    \end{macrocode}
+% 
+%
+% \bigskip
+% The control sequence |\@@_create_nodes:| is used twice: for the construction of the ``medium nodes'' and for the
+% construction of the ``large nodes''. The nodes are constructed with the value of all the dimensions 
+% \texttt{l_@@_row_\textsl{i}_min_dim}, \texttt{l_@@_row_\textsl{i}_max_dim}, 
+% \texttt{l_@@_column_\textsl{j}_min_dim} and \texttt{l_@@_column_\textsl{j}_max_dim}. Between the 
+% construction of the ``medium nodes'' and the ``large nodes'', the values of these dimensions are changed.
+%     \begin{macrocode}
+\cs_new_protected:Nn \@@_create_nodes:
+      {\int_step_variable:nnnNn \l_@@_nb_first_row_int 1 \g_@@_row_int \@@_i
+          {\int_step_variable:nnnNn 1 1 \g_@@_column_total_int \@@_j
+%    \end{macrocode}
+% We create two ponctual nodes for the extremities of a diagonal of the rectangular node we want to create. These
+% nodes |(@@~south~west)| and |(@@~north~east)| are not available for the user of \pkg{nicematrix}. That's why
+% their names are independent of the row and the column. In the two nested loops, they will be overwritten until the
+% last cell.
+%    \begin{macrocode}
+              {\coordinate (@@~south~west) 
+                           at (\dim_use:c {l_@@_column_\@@_j _min_dim},
+                               \dim_use:c {l_@@_row_\@@_i _min_dim}) ; 
+               \coordinate (@@~north~east) 
+                           at (\dim_use:c {l_@@_column_\@@_j _max_dim},
+                               \dim_use:c {l_@@_row_\@@_i _max_dim}) ; 
+%    \end{macrocode}
+% We can eventually draw the rectangular node for the cell (|\@@_i|-|\@@_j|). This node is created with the Tikz library
+% \pkg{fit}. Don't forget that the Tikz option |name suffix| has been set to |-medium| or |-large|.
+%    \begin{macrocode}
+               \draw node [fit = {(@@~south~west) (@@~north~east)},
+                           inner~sep=0pt,
+                           name = nm-\int_use:N \g_@@_env_int-\@@_i-\@@_j,
+                           alias = \tl_if_empty:NF \g_@@_name_tl 
+                                         {\tl_use:N \g_@@_name_tl-\@@_i-\@@_j}] 
+                          {} ; 
+              }
+          }
+%    \end{macrocode}
+% Now, we create the nodes for the cells of the |\multicolumn|. We recall that we have stored in
+% |\g_@@_multicolumn_cells_seq| the list of the cells where a |\multicolumn{|$n$|}{...}{...}| with $n$>1 was issued
+% and in |\g_@@_multicolumn_sizes_seq| the correspondant values of $n$.
+%    \begin{macrocode}
+      \@@_seq_mapthread_function:NNN \g_@@_multicolumn_cells_seq 
+                                     \g_@@_multicolumn_sizes_seq
+                                     \@@_node_for_multicolumn:nn
+      }
+%    \end{macrocode}
+%
+%
+% 
+%    \begin{macrocode}
+\cs_set:Npn \@@_extract_coords: #1-#2\q_stop{\cs_set:Npn \@@_i {#1} 
+                                             \cs_set:Npn \@@_j {#2}}
+%    \end{macrocode}
+%
+% The command |\@@_node_for_multicolumn:nn| takes two arguments. The first is the position of the cell where the
+% command |\multicolumn{|$n$|}{...}{...}| was issued in the format $i$|-|$j$ and the second is the value of~$n$ (the
+% length of the ``multi-cell'').
+%    \begin{macrocode}
+\cs_new_protected:Nn \@@_node_for_multicolumn:nn
+       {\@@_extract_coords: #1\q_stop
+        \coordinate (@@~south~west) 
+                    at (\dim_use:c {l_@@_column_\@@_j _min_dim},
+                        \dim_use:c {l_@@_row_\@@_i _min_dim}) ; 
+        \coordinate (@@~north~east) 
+                    at (\dim_use:c {l_@@_column_\int_eval:n{\@@_j+#2-1}_max_dim},
+                        \dim_use:c {l_@@_row_\@@_i _max_dim}) ; 
+        \draw node [fit = {(@@~south~west) (@@~north~east)},
+                    inner~sep=0pt,
+                    name = nm-\int_use:N \g_@@_env_int-\@@_i-\@@_j,
+                    alias = \tl_if_empty:NF \g_@@_name_tl 
+                                  {\tl_use:N \g_@@_name_tl-\@@_i-\@@_j}] 
+                   {} ; 
+        }
+%    \end{macrocode}
+%
+%
+% \subsection{We process the options}
+%
+% We process the options when the package is loaded (with |\usepackage|) but we recommend to use
+% |\NiceMatrixOptions| instead. 
+%
+% We must process these options after the definition of the environment |{NiceMatrix}| because the option
+% |renew-matrix| execute the code |\cs_set_eq:NN \env@matrix \NiceMatrix|. 
+%
+% Of course, the command |\NiceMatrix| must be defined before such an instruction is executed.
+%    \begin{macrocode}
+\ProcessKeysOptions {NiceMatrix}
+%    \end{macrocode}
+%
+% \subsection{Code for \texttt{seq_mapthread_function:NNN}}
+%
+% In |\@@_create_nodes:| (used twice in |\@@_create_extra_nodes:| to create the ``medium nodes'' and ``large
+% nodes''), we want to use |\seq_mapthread_function:NNN| which is in \pkg{l3candidates}). For security, we define a
+% function |\@@_seq_mapthread_function:NNN|. We will delete the following code when |\seq_mapthread_function:NNN|
+% will be in \pkg{l3seq}.
+%    \begin{macrocode}
+\cs_new:Npn \@@_seq_mapthread_function:NNN #1#2#3
+  {\group_begin:
+%    \end{macrocode}
+% In the group, we can use |\seq_pop:NN| safely.
+%    \begin{macrocode}
+   \int_step_inline:nnnn 1 1 {\seq_count:N #1}
+         {\seq_pop:NN #1 \l_tmpa_tl
+          \seq_pop:NN #2 \l_tmpb_tl
+          \exp_args:NVV #3 \l_tmpa_tl \l_tmpb_tl}
+   \group_end:
+  }
+%    \end{macrocode}
+%
+%    \begin{macrocode}
+\cs_set:Nn \@@_renew_matrix:
+    {\RenewDocumentEnvironment {pmatrix} {}
+         {\begin{pNiceMatrix}}
+         {\end{pNiceMatrix}}
+     \RenewDocumentEnvironment {vmatrix} {}
+         {\begin{vNiceMatrix}}
+         {\end{vNiceMatrix}}
+     \RenewDocumentEnvironment {Vmatrix} {}
+         {\begin{VNiceMatrix}}
+         {\end{VNiceMatrix}}
+     \RenewDocumentEnvironment {bmatrix} {}
+         {\begin{bNiceMatrix}}
+         {\end{bNiceMatrix}}
+     \RenewDocumentEnvironment {Bmatrix} {}
+         {\begin{BNiceMatrix}}
+         {\end{BNiceMatrix}}}
+%    \end{macrocode}
 % 
 % \section{History}
 %
 % \subsection{Changes between versions 1.0 and 1.1}
 % 
-% Option |silent| (with this option, the impossible instructions are discarded silently).
-%
 % The dotted lines are no longer drawn with Tikz nodes but with Tikz circles (for efficiency).
 % 
 % Modification of the code which is now twice faster.
@@ -3144,8 +4054,6 @@ version 2005/12/01 or later.
 %
 % New environment |{pNiceArrayC}| and its variants.
 %
-% We decrement |\g_@@_row_int| in |\@@_draw_lines:| to have the exact number of rows.
-% 
 % Correction of a bug in the definition of |{BNiceMatrix}|, |{vNiceMatrix}| and |{VNiceMatrix}| (in fact, it was a
 % typo).
 %
@@ -3166,9 +4074,16 @@ version 2005/12/01 or later.
 % \subsection{Changes between version 1.4 and 2.0}
 % 
 % The versions 1.0 to 1.4 of \pkg{nicematrix} were focused on the continuous dotted lines whereas the version 2.0 of
-% \pkg{nicematrix} provides differents features to improve the typesetting of mathematical matrices.
+% \pkg{nicematrix} provides different features to improve the typesetting of mathematical matrices.
+%
+% \subsection{Changes between version 2.0 and 2.1}
+%
+% New implementation of the environment |{pNiceArrayRC}|. With this new implementation, there is no restriction on
+% the width of the columns.
 %
+% The package \pkg{nicematrix} no longer loads \pkg{mathtools} but only \pkg{amsmath}.
 %
+% Creation of ``medium nodes'' and ``large nodes''.
 % \endinput
 % Local Variables:
 % TeX-fold-mode: nil
-- 
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