如何使用正则表达式（expl3）删除宏的最后一个字符？

Question

我正在尝试删除%我添加到按序列存储的宏中的符号，以防止在使用处理参数时(^M/ASCII-Return)添加该符号。TeX\scantokens

一切都很完美，但是，通过使用，\meaning我想删除%我在末尾添加的符号。在我的示例中，输出为：

Using \verb+\Scontents+ command,verbatim support, using balanced
braces, save in seq nospaceafter with index $1$.No space after close
:)%

我想要的是：

Using \verb+\Scontents+ command,verbatim support, using balanced
braces, save in seq nospaceafter with index $1$.No space after close
:)

这是我的示例文件：

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\keys_define:nn { scontents }
  {
    store-cmd .tl_set:N  = \l__scontents_name_seq_cmd_tl,
    store-cmd .initial:n = contents,
  }
\cs_new_protected:Npn \__scontents_append_contents:nn #1#2
  {
    \seq_if_exist:cF { g__scontents_seq_name_#1_seq }
      { \seq_new:c { g__scontents_seq_name_#1_seq } }
    \seq_gput_right:cn { g__scontents_seq_name_#1_seq } {#2}
  }
\cs_new:Npn \__scontents_getfrom_seq:nn #1#2
  {
    \seq_item:cn { g__scontents_seq_name_#2_seq } {#1}
  }
\exp_args_generate:n { Vx }
% stored
\ProvideDocumentCommand{ \Scontents }{ O{} +v }
  {
    \group_begin:
    \IfNoValueF {#1} { \keys_set_known:nn { scontents } {#1} }
    \tl_set:Nn \l_tmpa_tl {#2}
    \regex_replace_all:nnN { \^^M } { \^^J } \l_tmpa_tl
    \exp_args:NVx \__scontents_append_contents:nn \l__scontents_name_seq_cmd_tl
      { \exp_not:N \tex_scantokens:D { \tl_use:N \l_tmpa_tl \c_percent_str} }
    \group_end:
  }
% get
\ProvideDocumentCommand{ \getstored } { O{1} m }
  { 
    \__scontents_getfrom_seq:nn {#1} {#2} 
  }

% meaning
\ProvideDocumentCommand{ \meaningsc } { O{1} m }
  {
    \group_begin:
    \tl_set:Nx \l_tmpb_tl { \__scontents_getfrom_seq:nn {#1} {#2} }
    \regex_replace_once:nnN { ^ \c{tex_scantokens:D} \cB. (\c[^BE].*) \cE. } { \1 } \l_tmpb_tl
    \regex_replace_all:nnN { \v{1,} } { } \l_tmpb_tl
    % this not work
    \tl_reverse:N \l_tmpb_tl % reverse
    \tl_remove_once:Nn \l_tmpb_tl { \c_percent_str } % remove 
    \tl_reverse:N \l_tmpb_tl % reverse
    \ttfamily
    \cs_replacement_spec:N \l_tmpb_tl
    \group_end:
  }
\ExplSyntaxOff

\begin{document}
\Scontents[store-cmd=nospaceafter]{Using \verb+\Scontents+ command, 
verbatim support, using balanced braces, save in seq nospaceafter with index $1$.

No space after close :)}

\Scontents[store-cmd=nospaceafter]|Using \verb+\Scontents+ command, 
delimited by tbar, save in seq nospaceafter with index $2$. end by \verb+%+
\begin{verbatim*}
      verbatim environment
      with unbalanced } braces } 
\end{verbatim*}
No space after close, one percent at end of line%|

\noindent\hrulefill

XX\getstored[1]{nospaceafter}.No space after :) YY\par

\noindent\hrulefill

XX\getstored[2]{nospaceafter}.No space after :) YY

\noindent\hrulefill

\meaningsc[1]{nospaceafter}

\noindent\hrulefill

\meaningsc[2]{nospaceafter}

\end{document}

我尝试过使用\tl_reverse:N，但没有效果，我想也许可以用一些方法来实现regex（对此我不太确定）。

问候语