\NeedsTeXFormat{LaTeX2e}[1994/12/01]
\ProvidesPackage{ifnextok}[2011/06/27 v0.3 test next token (UL)]

%% Copyright (C) 2011 Uwe Lueck, 
%% http://www.contact-ednotes.sty.de.vu 
%% -- author-maintained in the sense of LPPL below -- 
%%
%% This file can be redistributed and/or modified under 
%% the terms of the LaTeX Project Public License; either 
%% version 1.3c of the License, or any later version.
%% The latest version of this license is in
%%     http://www.latex-project.org/lppl.txt
%% We did our best to help you, but there is NO WARRANTY. 
%%
%% Please report bugs, problems, and suggestions via 
%% 
%%   http://www.contact-ednotes.sty.de.vu 
%%
%% == Outline ==
%% The 'ifnextok' package deals with the behavior of 
%% \LaTeX's internal `\@ifnextchar' to skip blank spaces. 
%% This sometimes has surprising or for some users really 
%% \emph{unwanted} effects, especially with brackets following 
%% `\\' when                    %% v0.1a: was `where'
%% the user does \emph{not} intend to specify an 
%% optional argument, rather wants that brackets are \emph{printed.} 
%% The package offers commands and options for modifying this 
%% behavior, maybe limited to certain parts of the 
%% document source. They are described in the sections below 
%% together with the presentation of the implementation.
%% 
%% As after multiletter commands blank spaces are skipped anyway 
%% (\TeX book p.~46f.), the package makes a \emph{difference only 
%% for one-symbol commands} such as |\\|, or for %% \emph 2011/05/27
%% \emph{active characters} such as the double quote with 
%% \ctanpkgref{german}`.sty' and \ctanpkgref{babel}.
%% (v0.21: Or also optional arguments 
%%  \emph{following mandatory ones}---``trailing" optional arguments 
%%  mentioned by Lars Hellstr\"om and Bruno Le Floch on `LATEX-L'. 
%%  v0.21a: Moreover, with ``starred" command versions having a 
%%  first optional argument!)   %% 2011/06/14
%% 
%% Similar things happen in \ctanpkgref{amsmath} and 
%% \ctanpkgref{mathtools}, and as of v0.21,     %% v0.21a 2011/06/14
%% we discuss relations to these packages.
%% 
%% A little \strong{overview} of the package's commands and options:
%%                               %% structured 2011/05/27
%% === For Macro Writers ===
%% \begin{enumerate}
%%  \item |\IfNextToken| is an alternative to `\@ifnextchar', 
%%      not skipping spaces (\secref{main}). 
%%      This macro is the \strong{low-level} 
%%      backbone of all other modifications of \LaTeX\ commands.
%%  \item |\IfStarNextToken| is an alternative to `\@ifstar', 
%%      not skipping spaces, using `\IfNextToken' in lieu of 
%%      `\@ifnextchar' (\secref{star}).
%%  \item Some ``\strong{patching}" commands aim at modifying 
%%      existing (\LaTeX) macros without specifying the resulting 
%%      new definition explicitly 
%%      (Sections~\ref{sec:patch} and \ref{sec:star}). 
%%      As a package writer, 
%%      you just must know which macros need to be modified
%%      and specify their names as arguments for the patching macros. 
%%  \item There are low-level commands 
%%      |\INTstore| and |\INTrestore|
%%      for undoing modifications of existing macros 
%%      (\secref{stored}).
%% \end{enumerate}
%%
%% === For End-Users ===
%%  % \item 
%%      There are \strong{high-level} commands for modifying 
%%      |\\| and selecting \LaTeX\ \strong{environments} 
%%      to be affected (\secref{break}). 
%%      Package \strong{options} execute some of them 
%%      (\secref{options}), e.g., `[stdbreaks]'.
%%
%% === Intermediate ===
%% |\MakeNotSkipping{<target>}{<on-space>}| 
%% described in \secref{genpatch} is somewhat ``intermediate." 
%% It acts on a document-level command <target> without 
%% any assumptions about its internals. 
%% On the other hand, choosing <on-space> for the new behavior 
%% of <target> in front of a space token may need some knowledge ...
%%
%% (TODO: how command names are composed)   %% 2011/05/23, v0.1
%% 
%%   \pagebreak                                 %% 2011/06/26
%% == Caveats ==
%% \begin{enumerate}
%% \item Testing has not been very comprehensive so far. 
%% % \item 
%%       Usage together with \textcolor{blue}{\ctanpkgref{amsmath}}
%%       may require special care or fail altogether.
%% \item Switching into ``don't-skip-spaces" mode 
%%       \emph{two times} without switching back into normal mode 
%%       in between won't work with this version (v0.1--v0.3 TODO)
%%       of the package (TODO: permanent aliases).
%%       You will get the 
%%       \[\texttt{Argument of <patching> has an extra }`}.'\]
%%       error. This also applies to commands that have been issued 
%%       by package options.
%% \item Implementation may change much. 
%%       % , and certain auxiliary 
%%       % commands may move to separate packages. 
%%       (TODO 0.3)
%% \end{enumerate}
%%
%% == For Making Macros ==                      %% 2011/05/27
%% \label{sec:mac}
%% === The Main Command &\IfNextToken ===       %% & 2011/05/27
%% \label{sec:main}
%% |\IfNextToken<match>{<if>}{<else>}| %% add. miss. `\' 2011/05/31
%% is the obvious variant 
%% of \LaTeX's internal `\@ifnextchar' executing <if> 
%% if actually the \emph{``very next"} token is 
%% <match>                      %% v0.1a: was `mathc'
%% and executing <else> otherwise. If <match> is \emph{not} 
%% a \emph{space token} (\LaTeX's `\@sptoken') but 
%% the next token \emph{is}, <else> is executed; 
%% while `\@ifnextchar' tries matching the next token 
%% after ensuing space tokens. 
\newcommand{\IfNextToken}[3]{%
    \let\nextok@match= #1% 
%% ... v0.21 adds \qtd{`= '} after Heiko Oberdiek's explanation 
%% on \texhaxpref{11-05-017590}{texhax},        %% 2011/06/14
%% this allows `\@sptoken' as a possible `#1'. 
    \def\nextok@if{#2}\def\nextok@else{#3}%
    \futurelet\@let@token\nextok@decide}
%% ... apart from using different names, this is the same as 
%% `\new@ifnextchar' in `amsgen.sty' of the \ctanpkgref{amsmath}
%% bundle:
%% \begin{verbatim}
%% \long\def\new@ifnextchar#1#2#3{%
%%   \let\reserved@d= #1%
%%   \def\reserved@a{#2}\def\reserved@b{#3}%
%%   \futurelet\@let@token\new@ifnch
%% }
%% \end{verbatim}
%% ... and the behavior is essentially the same ...
\def\nextok@decide{%
    \ifx\@let@token\nextok@match \expandafter\nextok@if
    \else                        \expandafter\nextok@else
    \fi}
%% The analogue to our `\nextok@decide' in 'amsmath'/`amsgen.sty' 
%% is `\new@ifnch': 
%% \begin{verbatim}
%% \def\new@ifnch{%
%%   \ifx\@let@token\reserved@d \let\reserved@b\reserved@a \fi
%%   \reserved@b
%% }
%% \end{verbatim}
%%  ... and these two macros ('ifnextok''s and 'amsmath''s) 
%% actually make the difference to Standard \LaTeX. 
%% The latter's `\@ifnch' tests for `\@sptoken' before 
%% looking for the actually wanted `char', 'ifnextok'  and 
%% 'amsmath' don't. As to `\new@ifnch' vs.\ `\nextok@decide', 
%% the first has one token less than the latter, but one 
%% assignment more. What does this mean? TODO
%% 
%% When I decided to create the 'ifnextok' package, I was not aware 
%% of the similarity to 'amsmath', and I am not sure what I would 
%% have done had I ...
%%
%% |\NoNextSkipping| now switches into ``don't-skip-spaces" 
%% mode ``altogether" (however ...):
\newcommand*{\NoNextSkipping}{\let\@ifnextchar\IfNextToken}
%% This appears so dangerous to me that I don't want to support it 
%% much right now. |\RestoreNextSkipping| just switches back 
%% to \LaTeX's original version, so some support for 
%% \ctanpkgref{amsmath} may be missing here. 
\newcommand*{\RestoreNextSkipping}{%
    \let\@ifnextchar\kernel@ifnextchar}
%% Actually, because `\NoNextSkipping' does not affect 
%% `\kernel@ifnextchar', those of \LaTeX's commands using the latter 
%% still will skip spaces (with package version v0.1). 
%% 
%% As opposed to 'amsmath', 'ifnextok' aims at more choices 
%% as to what document-level commands are affected by the 
%% modified `next' checking. Of course, 'amsmath' deals with 
%% breaks between math display lines, while the present package 
%% rather was motivated by experiences in the humanities. 
%%
%% `\@sptoken' was discussed under \qtd{Some puzzling TeX} on 
%% texhax in 2011 (February/May/June), and the matter is discussed in 
%% \meta{The \TeX book} in Exercise~24.6 and on pp.~376f.
%%
%% === ``Bold" Patching Commands ===
%% \label{sec:patch}
%% % The little auxilary |\@xp@xp@xp| (cf.~`\@xp' in `amsgen.sty'):
%% % \providecommand*{\@xpxpxp}{\expandafter\expandafter\expandafter}
%% |\INTpatch<replacer><macro>| replaces 
%% something in the definition of <macro> according to 
%% the replacement macro <replacer>. 
%% This seems to work with the macros I thought of. 
%% It does \emph{not} work when 
%% (for replacing `\@ifnextchar')   %% mod. 2011/06/24:
%% (a)~there are \emph{more} `\@ifnextchar's in the 
%% macro to patch (outside braces), 
%% or when (b)~the only `\@ifnextchar' 
%% is inside a pair of braces.
\newcommand*{\INTpatch}[2]{%
  \expandafter\expandafter\expandafter \def
    \expandafter\expandafter\expandafter #2%
      \expandafter\expandafter\expandafter {%
        \expandafter #1#2}}                     %% red. 2011/06/24
%% |\NextTestPatch<macro>| replaces 
%% `\@ifnextchar' in the definition of <macro> by 
%% `\IfNextToken'. 
\newcommand*{\NextTestPatch}{\INTpatch\nextok@patch}
\def\nextok@patch#1\@ifnextchar{#1\IfNextToken} %% red. 2011/06/24
%% Another application of `\INTpatch' is `\StarTestPatch' in \secref{star}.
%% 
%% === Storing and Restoring ===
%% \label{sec:stored}
%% % |\WCS@namemod@apply@cs{<mod>}<apply>{<cs>}| 
%% % applies the token <apply> to (the token) <cs> modified by <mod>:
%% %\providecommand*\WCS@namemod@apply@cs[3]{%
%% %    \expandafter#2\csname#1#3\endcsname}
%% % Note the order of the arguments in the replacement text. 
%% % It allows shorthands like the following 
%% % |\INT@save@nmod<apply>{<cs>}|
%% % when one name modifyer is used for various purposes:
%% % \newcommand*{\INT@save@nmod}{\WCS@namemod@apply@cs\INT@save}
%% |\INTstore<macro>| stores the meaning of the macro <macro> 
%% in a special name space. 
%% %\newcommand*{\INTstore}[1]{\INT@save@nmod\let#1#1} 
\newcommand*{\INTstore}[1]{%
    \expandafter\let\csname\INT@save#1\endcsname#1}
%% In order to apply `\MakeNotSkipping' even to 
%% active characters below (v0.2), nothing must be gobbled 
%% from `\string<token>':
%% % `\INT@save<token>' is a \emph{``name modifier":}
% \newcommand*{\INT@save}{INT.save\expandafter\@gobble\string}
\newcommand*{\INT@save}{INT.save\string}
%% % For restoring, we use another general auxiliary 
%% % \[|\WCS@namemod@copy@to@from{<mod>}<new>{<old>}|:\]
%% %\providecommand*{\WCS@namemod@copy@to@from}[3]{%
%% %    \expandafter\let\expandafter#2\csname#1#3\endcsname}
%% % \providecommand*{\WCS@namemod@copy@to@from}[2]{%
%% %     \def\WCS@apply{\let#2}%
%% %     \WCS@namemod@apply@cs#1\WCS@apply}
%% |\INTrestore<macro>| \emph{re}stores the meaning of <macro> 
%% that is expected to have been stored with `\INTstore':
%% %\newcommand*{\INTrestore}[1]{\WCS@namemod@copy@to@from\INT@save#1#1}
\newcommand*{\INTrestore}[1]{%
    \expandafter\let\expandafter#1\csname\INT@save#1\endcsname}
%%
%% === The Star Test ===
%% \label{sec:star}
%% Before a \LaTeX\ line-break command tests for an optional argument, 
%% it tests for a star using `\@ifstar', which in turn invokes 
%% `\@ifnextchar'. So already `\@ifstar' needs to be modified. 
%% We do not so much want to change `\@ifstar' altogether, 
%% rather we will replace it at some places by a non-skipping 
%% variant |\IfStarNextToken|,\footnote{TODO or &\IfNextStar, 
%%                                      cf.~&\IfNextSpace.} 
%% using the patching command |\StarTestPatch<macro>|.
%% (`\@ifstar' has an argument and therefore cannot be patched as 
%%  nicely as the line-break commands.)
\newcommand*{\IfStarNextToken}[1]{\IfNextToken*{\@firstoftwo{#1}}}
\newcommand*{\StarTestPatch}{\INTpatch\nextok@starpatch}
%% The macro to be patched may contain a \cs{par} 
%% (`\@centercr' is an example), so we need `\long':
%%  %% red. 2011/06/24
\long\def\nextok@starpatch#1\@ifstar{#1\IfStarNextToken}
%% |\StoreStarSkipping| stores the current meaning of 
%% `\@ifstar' ...
%% % is executed before changing `\@ifstar' temporarily:
\newcommand*{\StoreStarSkipping}{\INTstore\@ifstar}
%% ... so that it can be restored by |\RestoreStarSkipping|:
\newcommand*{\RestoreStarSkipping}{\INTrestore\@ifstar}
%% |\NoStarSkipping| renders `\@ifstar' non-skipping altogether:
\newcommand*{\NoStarSkipping}{\let\@ifstar\IfStarNextToken}
%% This again seems to be so dangerous that it will not be 
%% supported much with package version v0.1 (by a package option). 
%% 
%% On the other hand, 'amsmath' (`amsgen.sty') is not as scrupulous 
%% as we are and indeed redefines `\@ifstar' \emph{altogether},
%% equivalent to our `\NoStarSkipping', except that the latter 
%% provides a method to restore. I.e., as soon as you have loaded
%% `amsgen.sty' (invoked by any 'amsmath' package), 
%% you have decided that a star appearing after 
%% whitespace is printed as a star, rather than choosing the 
%% ``starred" version of the respective command.
%% %% v0.21a 2011/06/14:
%% What we actually find in `amsgen.sty' is
%% \begingroup \hfuzz=33pt
%% \begin{verbatim}
%% \def\@ifstar#1#2{\new@ifnextchar *{\def\reserved@a*{#1}\reserved@a}{#2}}
%% \end{verbatim}
%% \endgroup \noindent
%% The `\reserved@a' trick seems to be due to 'amsmath''s idea 
%% of implementing the conditional 
%% (see the code we are quoting in \secref{main}).
%%
%% === More General Patching with \cs{@sptoken} ===
%% \label{sec:genpatch}
%% This section deals with modifying macros by a more general 
%% technique than employed in \secref{patch}. We do not use any 
%% knowledge of internals of the target user command 
%% (a ``control symbol" like `\\' or an ``active character"), 
%% and the command may take arguments, as the active double quote 
%% does with 'german.sty' or 'babel'.
%%
%% ==== &\IfNextSpace ====
%% |\IfNextSpace{<if>}{<else>}| is an auxiliary macro that 
%% executes <if> if the next token is a space token 
%% (\LaTeX's `\@sptoken'), otherwise it executes <else>:
\newcommand*{\IfNextSpace}{\IfNextToken\@sptoken}
%% This did not work with the v0.2 version of `\IfNextToken' 
%% that didn't have \qtd{`= '}, due to `\@sptoken' being an 
%% ``implicit space token," as Heiko Oberdiek pointed out 
%% on texhax. He also provided the remedy that actually was 
%% 'amsmath''s way ...
%%
%% v0.2 was:
%% \begin{verbatim}
%% \newcommand*{\IfNextSpace}[2]{%
%%     \def\nextok@if{#1}\def\nextok@else{#2}%
%%     \futurelet\@let@token\nextok@ifspace}
%% \newcommand*{\nextok@ifspace}{%
%%     \ifx\@let@token\@sptoken \expandafter \nextok@if
%%     \else                    \expandafter \nextok@else
%%     \fi}
%% \end{verbatim}
%% ... not so bad from an efficiency point of view, but ...---% 
%% % Is `\IfNextSpace' useful? I don't know of a shorthand 
%% % like `\@ifnextcharleftbracket' for   %% 2011/06/24 \qtd:
%% % \qtd{&\@ifnextchar[} ...             %% rm. 2011/06/26
%%
%% ==== &\MakeNotSkipping ====
%% |\MakeNotSkipping{<target>}{<on-space>}| should modify `<target>'
%% so that it acts in its usual way when no space token is ahead 
%% while executing <on-space> otherwise. E.g., <target> may be 
%% the active double quote |"| from 'babel', and on the left of a space 
%% token you want that the double quote just prints an ordinary 
%% double quote from the ligature 
%% \lq\verb+''+\rq\                 %% \ 2011/06/03
%% (the first pair of argument braces may be omitted):
%% \[\verb+\MakeNotSkipping{"}{''}+\] 
%% ... while I don't really recommend this right now (v0.2f.). 
%% %% rm. 2011/06/27 useless:
%% % For some unknown |\\|, 
%% % you may want to block searching for an optional argument by 
%% % \[`\MakeNotSkipping{\\}{\\\relax}'\]
%% 
%% <target>, being on document level and probably appearing 
%% in moving arguments, must be robust, while `\IfNextSpace' is not. 
%% When <target> has been defined using `\DeclareRobustCommand'
%% (`\\' from the `document' environment is an example), 
%% we would loose the original behavior of <target> if we used 
%% `\DeclareRobustCommand' ourselves. 
%%
%% v0.21 was horribly flawed at this point; I had not tested 
%% all cases, I had not studied how \LaTeX's `\DeclareRobustCommand' 
%% handles control symbols (such as `\_', see `source.pdf'), 
%% and my implementation did not obey the warning in my 
%% ancompanying documentation ...
%%
%% % |\RobustDeferName<cs>| may move to a general package 
%% % about robust commands TODO:
%% %\providecommand*{\RobustDeferName}[1]{\expandafter\@gobble\string#1 }
%% When <target> is a single (active) character, 
%% it may have been robustified by making it expand 
%% to a robust control sequence token, such as `~' 
%% via `\nobreakspace{}'---we don't know, 
%% or don't try to find out now. We make it robust, 
%% accepting that this may just introduce an unnecessary extra 
%% macro. %% rest of paragraph was nonsense 2011/06/27
\newcommand*{\INT@modified}[1]{%
    \ifx\protect\@typeset@protect 
        \expandafter\expandafter\expandafter \IfNextSpace
            \csname\INT@mod#1\expandafter\endcsname
    \else 
        \protect#1%
    \fi}
%% `\INT@mod<cs>' is another \emph{``name modifier":}
%% % `\WCS@namemod@apply@cs' from \secref{stored} 
%% % provides both arguments for `\IfNextSpace' associated with 
%% % #1 (TODO!?):
%% %     \edef\@tempa{\WCS@namemod@apply@cs\INT@mod\noexpand#1}%
%% %     \expandafter\expandafter\expandafter \IfNextSpace \@tempa}
\newcommand*{\INT@mod}{INT@mod.\string}
%% Here is the main command of the section. 
%% `\@tempa' will store the meaning of the command that <target> 
%% would call in typesetting mode after 
%% `\DeclareRobustCommand<target>'.
%% `\@tempb' will store what <target> does in in typesetting 
%% mode, maybe that is just the meaning of <target> 
%% (kind of flag, like `\if@tempswa'):
\newcommand*{\MakeNotSkipping}[2]{%
    \expandafter \let \expandafter \@tempa
        \csname\expandafter\@gobble\string#1 \endcsname
    \let\@tempb#1%
%% When #1 is a control word, and its name, extended by a space, 
%% is the name of a defined token, we \emph{lazily} 
%% (like \ctanpkgref{makerobust}, TODO) assume that 
%% its current meaning was assigned by `\DeclareRobustCommand'.
%% One exception: if that token is the control space~`\ ', 
%% #1 is a single character (hopefully active, TODO check!?).
    \ifx\@tempa\relax \else \ifx\@tempa\ \else
        \let\@tempb\@tempa \fi \fi
    \expandafter\let\csname\INT@save#1\endcsname\@tempb
%% We have analyzed #1 and now may modify it:
    \def#1{\INT@modified#1}%
%% We do not know beforehand what <on-space> will contain, 
%% in any case it should \emph{not} be expanded right here, 
%% that's why we use the token register `\@toks':
    \toks@{#2}%
    \expandafter\edef\csname\INT@mod#1\endcsname{%
        {\the\toks@}%
        \expandafter\noexpand\csname\INT@save#1\endcsname}%
}
%% This still is experimental, and you must care not to apply 
%% the patch two times when it has not been undone in between. 
%% The main application may be a macro like |\\| that some 
%% (non-standard) environment defines; then you could redefine 
%% the environmont so that its start finally modifies that 
%% macro according to your wishes. In the latter situation, 
%% the end of the environment will undo your `\MakeNotSkipping'; 
%% 
%% TODO: %% v0.2
%% In the case of |"|, this might be a starting point 
%% for handling conventions about moving an ensuing 
%% punctuation mark to the left of the quotation mark. 
%% Moreover, getting something really useful would require 
%% dealing with `"' at the left of a bracket too.
%%
%% %  \pagebreak                                 %% 2011/06/26
%% == ``Manual" Line Breaks ==
%% \label{sec:break}
%% === Outline of Implementation ===
%% In the first instance, the present package aims at rendering 
%% |\\| a command that interpretes a left-hand square bracket 
%% as a start of an optional argument only if the bracket is not 
%% preceded by any other token (apart from the star in `\\*'), 
%% especially not by a space token. 
%% 
%% Indeed, an author may expect that when a bracket opens in a 
%% \emph{different} line than the `\\', then it will be 
%% \emph{printed} rather than interpreted as an 
%% \emph{optional-argument delimiter}
%% (the package author has been such an author some times). 
%% Now, when the bracket only is in a line \emph{following} 
%% the line carrying the `\\', the end-line character 
%% normally produces a space token (\TeX book p.~47), 
%% so the present idea of implementation will cover 
%% the case of a bracket in the next line.
%% 
%% In `latex.ltx', the names of the commands implementing the 
%% line break have some ``pivot" part <pivot> that we can use 
%% to patch them in a uniform way. They are two in each case: 
%% The first starts with `\@<pivot>' and invokes `\@ifstar', 
%% the second starts with `\@x<pivot>' and invokes the 
%% left-hand-bracket test. Both of them need to be patched. 
%% 
%% === ``Normal" Manual Line Breaks ===
%% \label{sec:newline}
%% If I had been aware of the difficulties of this part, 
%% I probably would not have started writing this package, 
%% hoping it would be the work of about an hour. 
%% 
%% `\@xnewline' must be patched in order to get a non-skipping
%% version of the bracket test, and this patch suffices for the 
%% optional-argument goal. 
%% 
%% %% more accurately 2011/05/31:
%% The `\@ifstar' call is in `\@normalcr' and its alias `\\ '; 
%% the latter is invoked by `\\' according to `\DeclareRobustCommand\\'.
%% 
%% Things seem to be easier when `\\ ' \emph{expands} to `\@normalcr' 
%% instead of being an \emph{alias} of it 
%% (\strong{\textcolor{blue}{CAUTION!}}).
%% Then we just need to control `\@normalcr':
\@namedef{\@backslashchar\space}{\@normalcr}
%% |\StoreNewlineSkipping| \emph{stores} the skipping behavior of |\\|
%% outside special environments:
\newcommand*{\StoreNewlineSkipping}{%
    \INTstore\@normalcr \INTstore\@xnewline}
%% |\RestoreNewlineSkipping| \emph{re}stores the skipping behavior of |\\|
%% outside special environments:
\newcommand*{\RestoreNewlineSkipping}{%
    \INTrestore\@normalcr \INTrestore\@xnewline}
%% |\NoNewlineSkipping| \emph{suppresses} skipping blank spaces with 
%% |\\| outside special environments:
\newcommand*{\NoNewlineSkipping}{%
    \StarTestPatch\@normalcr \NextTestPatch\@xnewline}
%%
%% === Manual Line Breaks in \LaTeX\ Environments ===
%% \label{sec:envs}
%% The macros in the present section should modify \LaTeX's |\\| 
%% in environments (<env> being one of:) 
%% |center|, |tab|, |array|, and |tabular|. 
%% These \emph{environment names} are the expected 
%% \emph{arguments} of those macros. 
%% However, argument |center| also affects the 
%% %% 2011/05/27 v0.11a verse:
%% |flushleft|, |flushright|, and 
%% |verse| environments,\footnote{`verse' 
%%      is provided by \LaTeX's standard \ctanpkgref{classes} only, 
%%      while `flushleft' and `flushright' belong to the \LaTeX\ 
%%      kernel.} 
%% and |array| and |tabular| should also affect 
%% their enhanced variants from other \LaTeX\ packages. 
%% When this internal structure of \LaTeX\ changes, 
%% the present section may become obsolete ...
%%
%% |\INTactOnEnv{<action1>}{<action2>}{<env>}| 
%% is the backbone of these macros. 
%% <action1> and <action2> are one of 
%% \[`\INTstore', `\INTrestore', `\StarTestPatch', 
%% `\NextTestPatch'.\] 
%% <action1> deals with `\@ifstar', 
%% <action2> deals with `\@ifnextchar':
\newcommand*{\INTactOnEnv}[3]{%
    \expandafter#1\csname  @#3cr\endcsname
    \expandafter#2\csname @x#3cr\endcsname}
%% |\StoreSkippingCRs{<env>}| \emph{stores} the skipping behavior 
%% of |\\| in environments <env>:
\newcommand*{\StoreSkippingCRs}{%
    \INTactOnEnv\INTstore\INTstore}
%% |\RestoreSkippingCRs{<env>}| \emph{re}stores the skipping behavior 
%% of |\\| in environments <env>:
\newcommand*{\RestoreSkippingCRs}{%
    \INTactOnEnv\INTrestore\INTrestore}
%% |\NotSkippingCRs{<env>}| \emph{suppresses} space skipping
%% of |\\| in environments <env>: 
\newcommand*{\NotSkippingCRs}{%
    \INTactOnEnv\StarTestPatch\NextTestPatch}
%% % \NotSkippingCRs{center}
%% \begin{center}
%%  % \MakeNotSkipping\\{\\\relax}
%%  %  \show\\
%%    Do these commands work?\\ [\,Or do they not?\,]
%% \end{center}
%% 
%% %% 2011/05/27 v0.11a:
%% By contrast, the environments |quotation| and |quote| 
%% from \LaTeX's standard \ctanpkgref{classes} use the 
%% ``normal" newline command essentially provided by 
%% `\@normalcr'.
%% === 'amsmath' and 'mathtools' ===
%% Just discussing related functionality in 
%% the \ctanpkgref{amsmath} and \ctanpkgref{mathtools}
%% packages, without any own code: 
%% %% modifications v0.21a 2011/06/14:
%% 
%% 'amsmath' modifies the star (|*|) test all over the document 
%% (see our \secref{star}), while providing own 
%% (not skipping) versions of |\\| rather in math displays 
%% and math environments only. This applies quite obviously 
%% to the `{cases}' and `{matrix}' environments. 
%% I am not sure about 'amsmath''s use of `\displaybreak',
%% (cf.~`amstex.sty' and the `\intertext' command) and `\math@cr'. 
%%
%% 'mathtools' modifies 'amsmath''s line breaking behavior 
%% in turn on its options `[allowspaces]' and `[disallowspaces]', 
%% referring to some strange behavior of 'amsmath'. 
%% Still I don't understand what is going on entirely, 
%% and my impression is that nobody else has understood these 
%% things entirely so far. 'mathtools' is not the first 
%% package suppressing space skipping with `\\', 'amsmath' has done 
%% this already; the question is where, where not, and why ... 
%% 'mathtools''s `[disallowspaces]' just seems to provide 
%% a more straightforward policy ... TODO
%% % Again, please see the 'mathtools' documentation for more details. 
%% %% <- rm. 2011/06/14 
%%
%% == Package Options ==
%% \label{sec:options} 
%% === Behavior \emph{without} Options ===
%% If the package is called without any option, 
%% it only defines `\IfNextToken', `\IfStarNextToken' 
%% and the other package-writer or user commands, 
%% without actually changing behavior of any \LaTeX\ command.
%%
%% === Option `newline' ===
%% Package option |newline| stores and disables space skipping for 
%% |\\| in ``normal" mode according to \secref{newline}:
\DeclareOption{newline}{\StoreNewlineSkipping\NoNewlineSkipping}
%% 
%% === Environments ===
%% The next package options are just the environment names 
%% according to \secref{envs} 
%% (|center|, |tab|, |array|, |tabular|).
%% Option |<env>| stores and disables the skipping behavior 
%% of |\\| in <env> environments. 
%% We abuse the our temporary macro `\nextok@match' from 
%% \secref{main}:
\def\nextok@match#1{%
    \DeclareOption{#1}{\StoreSkippingCRs{#1}\NotSkippingCRs{#1}}}
\nextok@match{center}
\nextok@match{tab}
\nextok@match{array}
\nextok@match{tabular}
%% === ``All Options" or ``Standard Options" ===
%% Package Options |all| and (v0.11:\@) |stdbreaks| have the same effect as 
%% using the `newline' option and the environment package options 
%% `center', `tab', `array', and `tabular' at once. 
\def\nextok@match#1{\csname ds@#1\endcsname}
%% (... must not be changed before `\ProcessOptions' ...)
\DeclareOption{all}{%
    \nextok@match{newline} \nextok@match{center}
    \nextok@match{tab} \nextok@match{array} \nextok@match{tabular}}
%% Behavior of option |all| may \emph{change} in the future of the package, 
%% while option |stdbreaks| should rather \emph{keep} its present behavior.
\DeclareOption{stdbreaks}{\nextok@match{all}}   %% v0.11
%%
%% 
%% == Processing Options and Leaving the Package ==
\ProcessOptions
\endinput
%%
%% == Acknowledgments ==                        %% v0.2 2011/05/27
%% While I experienced the problem myself some years ago with 
%% a critical edition, I finally decided to do this work 
%% after postings by Susan Dittmar (March 2011)     %% 017128
%% and Philipp Stephani (December 2010)             %% 106431
%% on the \texhaxref{}{'texhax'} mailing list.
%% The latter pointed to \ctanpkgref{mathtools}. 
%% 
%% Moreover, the space skipping matter was discussed on the 
%% `LATEX-L' mailing list (\qtd{xparse and space skipping}) 
%% in mid of May 2011, and the present 
%% package may be considered a contribution to that discussion 
%% (saying something like: keep the simple standard for beginners, 
%%  offer something advanced for advanced users if you think 
%%  some of them want it ... maybe just as `contrib').
%% Bruno Le Floch (May~11) and Frank Mittelbach (May~15)
%% made me aware of the similar functionality in 'amsmath'. 
%% Wordings in describing 'ifnextok' may resemble wordings 
%% in that `LATEX-L' very much. Only for v0.21, I actually 
%% read these `LATEX-L' postings, rather than only their 
%% subject lines.
%% 
%% See sections~\ref{sec:main} and~\ref{sec:genpatch} for 
%% Heiko Oberdiek's contribution.   %% 2011/06/24
%% 
%% == VERSION HISTORY ==
v0.1   2011/05/23   very first 
v0.11  2011/05/23   typo `mathc' fixed, where/when
       2011/05/27   &, more structure, option [stdbreaks]
       2011/05/27   doc. mentions `verse', `quotation', `quote'; 
                    ack.s
v0.2   2011/05/30   \IfNextSpace, \MakeNotSkipping 
       2011/05/31   using \@normalcr differently; 
                    corrected \IfNextSpace 
v0.21  2011/06/02   reworked \IfNextToken and \IfNextSpace 
                    after Heiko Oberdiek, regarding amsmath; 
                    documentation discusses amsmath and mathtools 
                    and refers to LATEX-L
       2011/06/03   ... \ , \rq\ ; corr. version string
v0.21a 2011/06/14   quoting \@ifstar from amsmath, extended comments 
                    on amsmath and mathtools, starred versions, 
                    Heiko Oberdiek for sec:main
       TO CTAN
v0.22  2011/06/24   ack's extended; reduced sec:patch; sec:genpatch: 
                    horribly fragile robustification fixed
       2011/06/25   re-implementations in sec:patch using \WCS...
       2011/06/26   was named v0.3, renamed v0.22
       JUST STORED
v0.3   2011/06/26   sec:stored as v0.11; 
                    sec:genpatch code similar to v0.2; 
                    different sectioning; \pagebreak's
       2011/06/27   \INT@modified streamlined, rm. useless \\ example 
                    and wrong description of \INT@modified