comment 包允许将给定的环境（我们称之为toto）设置为注释并使其内容消失。我怎样才能做到这一点，同时仍然有一个命令（我们称之为\keepthis{...}内部命令）正在执行？例如
\begin{toto}
Stuff which will disappear...
\keepthis{Something which must appear nevertheless}
Again stuff which will disappear...
\end{toto}
换句话说，我们如何才能拥有一个comment类似 - 的环境，它可以删除所有文本、数学、命令，只保留单个命令及其参数？这意味着comment不仅要搜索，\end{toto}还要搜索\keepthis{...}通过恢复所有 s 等来执行的内容\catcode，然后再次搜索两者，直到找到\end{toto}真正恢复所有内容的内容。这可能吗？
答案1
用于l3regex提取适当的标记列表。
\documentclass{article}
\usepackage{xparse,environ,l3regex}
\ExplSyntaxOn
\NewEnviron{toto}
{
\bool_if:NTF \g_yannis_toto_show_bool
{ \BODY }
{ \par \yannis_toto_keep:V \BODY }
}
\NewDocumentCommand{\showtoto}{}
{
\bool_gset_true:N \g_yannis_toto_show_bool
}
\NewDocumentCommand{\hidetoto}{}
{
\bool_gset_false:N \g_yannis_toto_show_bool
}
\bool_new:N \g_yannis_toto_show_bool
\seq_new:N \l__yannis_toto_keep_seq
\cs_new_protected:Nn \yannis_toto_keep:n
{
\regex_extract_all:nnN { \c{keepthis}\s*\cB..*?\cE. } { #1 } \l__yannis_toto_keep_seq
\seq_use:Nn \l__yannis_toto_keep_seq { \par }
}
\cs_generate_variant:Nn \yannis_toto_keep:n { V }
\ExplSyntaxOff
\newcommand{\keepthis}[1]{#1}
\begin{document}
\hidetoto
\section{One instance}
Here is a toto environment
\begin{toto}
Stuff which will disappear...
\keepthis{Something which must appear nevertheless}
Again stuff which will disappear...
\end{toto}
\section{Two instances}
Here is a toto environment
\begin{toto}
Stuff which will disappear...
\keepthis{Something which must appear nevertheless}
Again stuff which will disappear...
\keepthis{Something which must appear nevertheless}
Again stuff which will disappear...
\end{toto}
\showtoto
\section{One instance}
Here is a toto environment
\begin{toto}
Stuff which will disappear...
\keepthis{Something which must appear nevertheless}
Again stuff which will disappear...
\end{toto}
\section{Two instances}
Here is a toto environment
\begin{toto}
Stuff which will disappear...
\keepthis{Something which must appear nevertheless}
Again stuff which will disappear...
\keepthis{Something which must appear nevertheless}
Again stuff which will disappear...
\end{toto}
\end{document}
