Shared

<..theindex warning..>+
 \def\ind:defs{\let\LNKidx\empty
    \def\LNK##1##2##3##4{\ifx\NewConfigure\:UnDef\else
         \def\LNK:number{##4}%
         \a:LNK[##1]{##2}{}\gHAdvance\:LNKno1
            \def\:THIrd{##3}\ifx\:THIrd\empty
               \LNKidx{\ifx\c:LNK\empty\:LNKno\else \c:LNK\fi}\else
               \LNKidx{##3}\fi
            \global\let\LNKidx\empty
         \b:LNK
       \fi}%
    \def\:LNKno{0}}
 \NewConfigure{LNK}{3}
 \Configure{LNK}{\Link}{\EndLink}{}
 -_-_-

A ‘=’ in \let\LNKidx= is harmful.

<..open 4dx output files..>
 \newwrite\idx
 \newwrite\indexes
 \def\MakefileIn#1#2#3#4{#1.#3}
 \def\MakefileIndexes#1#2#3#4{#1.4ix}
 \immediate\openout\idx=\expandafter\MakefileIn\filename\relax
 \immediate\openout\indexes=\expandafter\MakefileIndexes\filename\relax
 -_-_-

<..close 4dx output files..>
 \immediate\closeout\idx
 \immediate\closeout\indexes
 -_-_-

<..idxmake.4ht..>
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % idxmake.4ht                          2014-07-12-22:36 %
 % Copyright (C) 2000--2009      Eitan M. Gurari         %
 <.TeX4ht copyright.>
 
 \def\SourceInd#1#2#3#4{#1.#2}
 \def\MakefileInd#1#2#3#4{#1.#4}
 
 \newcount\cnt
 \newtoks\split
 
 \def\noXcatcodes{%
    \cnt=0
    \def\noXXcatcodes{%
       \catcode\cnt12
       \ifnum\cnt<255
           \advance\cnt  1  \expandafter\noXXcatcodes
       \fi }%
    \noXXcatcodes }
 
 <.open 4dx output files.>
 \def\beforeentry#1#2#3#4{
    \def\file{#1}\def\anchor{#2}\def\pointer{#3}\def\indexentry{\string#4}
    \begingroup   \noXcatcodes
      \catcode‘\s=11 \catcode‘\e=11 ‘%for \see‘%
      \catcode‘\^^M=10    \catcode‘\ =10    \catcode‘\^^I=10
      \catcode‘\{=1 \catcode‘\}=2 \futurelet\next\preGetentries
 }
 \def\bparent#1|(#2<.par del.>{\def\core{#1}\def\parent{#2}}
 \def\eparent#1|)#2<.par del.>{\def\core{#1}\def\parent{#2}}
 \def\see#1|see#2|see#3<.par del.>{\def\preSee{#1}\def\isSee{#2}}
 <.regular index.>
 <.reverse index.>
 \input \expandafter\SourceInd\filename\relax
 <.close 4dx output files.>
 
 \bye
 \endinput
 -_-_-