可扩展宏，无需额外软件包即可提取 UTF-8/西里尔文或 UTF-8/ASCII 字符串中多个单词的第一个字符

Question 1

下面的操作就是你想要的。

我使用 L3 而不是 David 使用的低级来编码。基本思路仍然相同，如果它以扩展为的内容开头，\UTFviii@two@octets我们就收集这两个八位字节，否则我们只使用第一个字符。但是，这也用于\text_purify:n输入，以确保循环的输入仅为文本。

然后我们简单地在每个空格处进行分割（我们必须检查是否完成\quark_if_recursion_tail_stop:n）并获取第一个字符（或组成 UTF8 八位字节对的两个字符）。

该宏\firstofwords将其第一个参数作为每个单词首字母后应放置的内容，第二个参数是用空格分隔的单词列表。

\documentclass{article}

\usepackage[T2A]{fontenc}
\usepackage[russian]{babel}

\makeatletter
\newcommand{\firstof}[1]{\expandafter\checkfirst#1\@nil}
\def\checkfirst#1{%
  \ifx\UTFviii@two@octets#1%
  \expandafter\gettwooctets
  \else
  \expandafter\@car\expandafter#1%
  \fi
}
\def\gettwooctets#1#2#3\@nil{\UTFviii@two@octets#1#2}

\ExplSyntaxOn
\cs_new:Npn \crosfield_first_of_words:nn #1#2
  { \exp_not:e { \__crosfield_first_of_words:e { \text_purify:n {#2} } {#1} } }
\group_begin:
\cs_set:Npn \__crosfield_tmp:n #1
  {
    \cs_new:Npn \__crosfield_first_of_words:n ##1 ##2
      {
        \__crosfield_first_of_words_spaces:nw {##2} ##1 #1 % #1 is a space
          \q_recursion_tail #1 % #1 is a space
          \q_recursion_stop
      }
  }
\__crosfield_tmp:n { ~ }
\group_end:
\cs_generate_variant:Nn \__crosfield_first_of_words:n { e }
\makeatletter
\cs_new:Npn \__crosfield_first_of_words_spaces:nw #1 #2 ~
  {
    \quark_if_recursion_tail_stop:n {#2}
    \tl_if_head_eq_meaning:oNTF {#2} \UTFviii@two@octets
      { \__crosfield_first_of_words_aux:nnw #2 \q_stop }
      { \tl_head:n {#2} }
    \exp_not:n {#1}
    \__crosfield_first_of_words_spaces:nw {#1}
  }
\makeatother
\cs_generate_variant:Nn \tl_if_head_eq_meaning:nNTF { o }
% there can't be a \q_stop in the argument as that would've caused an infinite
% loop in \text_purify:n, so this is fine and faster than allowing arbitrary
% contents.
\cs_new:Npn \__crosfield_first_of_words_aux:nnw #1#2#3 \q_stop
  { \exp_not:n { #1#2 } }

% define a LaTeX2e name for the above function
\cs_new_eq:NN \firstofwords \crosfield_first_of_words:nn
\ExplSyntaxOff

\begin{document}

\firstof{Vladimir}

\firstof{Владимир}

\firstofwords{.\ }{Vladimir Владимир} example

\firstofwords{.}{foo bar baz}

\end{document}

编辑：如果您只需要第二个参数并且希望.每次都在第一个字母之间放置一个，则可以使用以下内容代替\cs_new_eq:NN \firstofwords \crosfield_first_of_words:nn：

\newcommand* \firstofwords { \crosfield_first_of_words:nn {.} }

编辑2：

此变体仅将第一个参数放置在\firstofwords元素之间，但不放置在最后一个参数之后。

\documentclass[varwidth,border=3.14]{standalone}

\usepackage[T2A]{fontenc}
\usepackage[russian]{babel}

\makeatletter
\newcommand{\firstof}[1]{\expandafter\checkfirst#1\@nil}
\def\checkfirst#1{%
  \ifx\UTFviii@two@octets#1%
  \expandafter\gettwooctets
  \else
  \expandafter\@car\expandafter#1%
  \fi
}
\def\gettwooctets#1#2#3\@nil{\UTFviii@two@octets#1#2}

\ExplSyntaxOn
\cs_new:Npn \crosfield_first_of_words:nn #1#2
  { \exp_not:e { \__crosfield_first_of_words:e { \text_purify:n {#2} } {#1} } }
\group_begin:
\cs_set:Npn \__crosfield_tmp:n #1
  {
    \cs_new:Npn \__crosfield_first_of_words:n ##1 ##2
      {
        \__crosfield_first_of_words_spaces:Nnw \use_none:n {##2} ##1 #1 % #1 is a space
          \q_recursion_tail #1 % #1 is a space
          \q_recursion_stop
      }
  }
\__crosfield_tmp:n { ~ }
\group_end:
\cs_generate_variant:Nn \__crosfield_first_of_words:n { e }
\makeatletter
\cs_new:Npn \__crosfield_first_of_words_spaces:Nnw #1 #2 #3 ~
  {
    \quark_if_recursion_tail_stop:n {#3}
    #1 {#2}
    \tl_if_head_eq_meaning:oNTF {#3} \UTFviii@two@octets
      { \__crosfield_first_of_words_aux:nnw #3 \q_stop }
      { \tl_head:n {#3} }
    \__crosfield_first_of_words_spaces:Nnw \exp_not:n {#2}
  }
\makeatother
\cs_generate_variant:Nn \tl_if_head_eq_meaning:nNTF { o }
% there can't be a \q_stop in the argument as that would've caused an infinite
% loop in \text_purify:n, so this is fine and faster than allowing arbitrary
% contents.
\cs_new:Npn \__crosfield_first_of_words_aux:nnw #1#2#3 \q_stop
  { \exp_not:n { #1#2 } }

% define a LaTeX2e name for the above function
\cs_new_eq:NN \firstofwords \crosfield_first_of_words:nn
\ExplSyntaxOff

\begin{document}

\firstof{Vladimir}

\firstof{Владимир}

:\firstofwords{.\,}{Vladimir Владимир}.:

\firstofwords{.}{foo bar baz}

\end{document}

如果你希望始终.\,在元素之间使用，并且.在最后一个元素之后使用，则可以使用

\newcommand\firstofwords[1]{ \crosfield_first_of_words:nn {.\,} {#1} . }

而不是\cs_new_eq:NN-line。

Answer

下面的操作就是你想要的。