让特殊项目标签在索引中被正确引用

Question

makeindex按键和页面对索引条目进行排序，因此它（似乎）要求每个页面都采用一种且仅一种“数字”形式（数字、阿拉伯和罗马）。

您的示例中的2*“数字”形式不是有效的，因此恐怕您必须进行页面封装（\index{<key>|<cmd>}), manually or automatically if you patch the\index` 内部）。

手动页面封装示例：

% define
\newcommand{\idxStarred}[1]{#1*}
% then use
\item[2*] Special item.\index{Special item|idxStarred}

注意这并不能解决所有问题。例如，排序时它无法使所有未加星号的索引条目小于加星号的索引条目。

更新：这次新尝试将“特殊页面”拆分为页面和页面辅助部分（使用l3regex），然后自动插入页面封装。因此

% input
\item[2*] Special item\index{special item}

% i) will generate, in `.idx` file
\indexentry{Special item|myindexPrintPage{*}}{2}

% ii) will become, in `.ind` file, after running `makeindex`
\item Special item, \myindexPrintPage{*}{2}

% iii) will finally typeset as, in `.pdf` file
Special item, 2*

\documentclass[openany]{book}
\usepackage{enumitem}
\usepackage{tcolorbox}

\usepackage{imakeidx}
\usepackage{idxlayout}
\makeindex

\ExplSyntaxOn
\tl_new:N \l_myindex_page_tl      % beginning digits
\tl_new:N \l_myindex_page_aux_tl  % anything left

\regex_const:Nn \c_begining_digits_regex { ^(\d+) }

\msg_new:nnn {myindex} {wrong-page-pattern}
  {Wrong page pattern ``\tl_to_str:n{#1}''}

% split special page into page_tl and page_aux_tl
% e.g. 
%   input: special page == "2*"
%   output: page_tl == "2", page_aux_tl == "*"
\cs_new:Nn \myindex_split_page:n
  {
    \regex_split:NnNTF \c_begining_digits_regex {#1} \l_tmpa_seq
      {
        % now the seq is "<empty>, page_tl, page_aux_tl"
        \seq_pop_right:NN \l_tmpa_seq \l_myindex_page_aux_tl
        \seq_pop_right:NN \l_tmpa_seq \l_myindex_page_tl
      }
      { \msg_error:nnn {myindex} {wrong-page-pattern} {#1} }
  }
\cs_generate_variant:Nn \myindex_split_page:n {V}

\makeatletter
\cs_set_eq:NN \myindexPrintPage \@swaptwoargs

\def\@wrindex#1#2{%
  \ifdefined\@currentitem
    \myindex_split_page:V \@currentitem
    \imki@wrindexentrysplit{#1}
      {#2|myindexPrintPage{\l_myindex_page_aux_tl}}
      {\l_myindex_page_tl}%
    \endgroup
    \imki@showidxentry{#1}{#2}%
  \else
    \imki@wrindexentrysplit{#1}{#2}{\arabic{enumi}}%
    \endgroup
    \imki@showidxentry{#1}{#2}%
  \fi
  \@esphack
}
\makeatother
\ExplSyntaxOff

\makeatletter
\let\olditem\item
\newcommand*{\purpleboxitems}{%
  \renewcommand*{\item}[1][]{%
    \ifblank{##1}
      {\let\@currentitem\@undefined\olditem}
      {\def\@currentitem{##1}\olditem[\purplebox{##1}]}%
  }%
}
\makeatother

\newtcbox{\purplebox}[1][]{nobeforeafter,
   notitle,
   colframe=purple!20!black,
   colback=purple!50!black,
   top=4pt,
   left=5pt,
   right=5pt,
   bottom=2pt,
   fontupper=\sffamily\bfseries,
   colupper=white,
   tcbox raise base,
   #1}

\setlist{
  label*={\purplebox{\arabic*}},
  before=\purpleboxitems,
  after=\let\item\olditem,
}

\begin{document}
\thispagestyle{empty}
\Large
\begin{enumerate}
  \item     Regular item.\index{First regular item}
  \item     Regular item.\index{Second regular item}
  \item[2*] Special item.\index{Special item}
  \item[2+] Another special item.\index{Special item}
  \item     Regular item.\index{Second regular item}
  \item[3$\neq$] Third special item.\index{Special item}
\end{enumerate}

\idxlayout{columns=1}
\printindex
\end{document}

Answer 1