From d6888fdb49e3ac954c2d436951f364d3a4a4b17d Mon Sep 17 00:00:00 2001
From: Norbert Preining <norbert@preining.info>
Date: Wed, 22 Jun 2022 03:01:02 +0000
Subject: CTAN sync 202206220301

---
 support/TeX4ht/source/ChangeLog      |  6 ++++++
 support/TeX4ht/source/tex4ht-4ht.tex | 30 ++++++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 2 deletions(-)

(limited to 'support/TeX4ht')

diff --git a/support/TeX4ht/source/ChangeLog b/support/TeX4ht/source/ChangeLog
index 5dfc905668..ef9c5510f6 100644
--- a/support/TeX4ht/source/ChangeLog
+++ b/support/TeX4ht/source/ChangeLog
@@ -1,3 +1,9 @@
+2022-06-21  Michal Hoftich  <michal.h21@gmail.com>
+
+	* tex4ht-4ht.tex (latex.4ht): fixed support for \index commands
+	inside \caption.
+	https://tex.stackexchange.com/a/647924/2891
+
 2022-06-20  Michal Hoftich  <michal.h21@gmail.com>
 
 	* tex4ht-4ht.tex (pdfpages.4ht): added support for the Pdfpages
diff --git a/support/TeX4ht/source/tex4ht-4ht.tex b/support/TeX4ht/source/tex4ht-4ht.tex
index 0c2e94ba1b..0c2bd00913 100644
--- a/support/TeX4ht/source/tex4ht-4ht.tex
+++ b/support/TeX4ht/source/tex4ht-4ht.tex
@@ -1,4 +1,4 @@
-% $Id: tex4ht-4ht.tex 1157 2022-06-20 13:49:01Z michal_h21 $
+% $Id: tex4ht-4ht.tex 1158 2022-06-21 15:56:07Z michal_h21 $
 % tex tex4ht-4ht   or   ht tex tex4ht-4ht
 %
 % Copyright 2009-2022 TeX Users Group    
@@ -11487,15 +11487,41 @@ The following has been changed for getting links in \`'.aux' files to
 \`'.lot' (list of tables) and \`'lof'  (list of figures) files.
 
 \<latex ltfloat\><<<
+|<latex caption index|>
 \long\def\:tempc#1[#2]#3{\par \cur:lbl{}%
   |<write caption to toc|>\begingroup
+    |<latex caption index save|>
     \@parboxrestore \normalsize
     \@makecaption{\csname fnum@#1\endcsname}{\ignorespaces #3}\par
-  \endgroup |<cancel if-label anchors|>}
+  \endgroup 
+|<latex caption index print|>
+|<cancel if-label anchors|>}
 \def\numberline#1{\hbox to\@tempdima{#1\hfil} }
 \HLet\@caption|=\:tempc
 >>>
 
+The index commands used inside caption may result in fatal error. 
+We use the LaTeX 3 sequences to save their contents inside caption,
+and print them when it is safe.
+
+\<latex caption index\><<<
+\ExplSyntaxOn
+\seq_new:N\:savedindex
+\def\:initsaveindex{\seq_gclear:N\:savedindex}
+\def\:saveindex#1{\seq_gput_right:Nn\:savedindex{#1}}
+\def\:printsavedindex{\seq_map_inline:Nn\:savedindex{\index{##1}}}
+\ExplSyntaxOff
+>>>
+
+\<latex caption index save\><<<
+\:initsaveindex%
+\let\index\:saveindex%
+>>>
+
+\<latex caption index print\><<<
+\:printsavedindex%
+>>>
+
 The \''|<cancel if-label anchors|>' request no 
 the \''\label' commands to avoid duplicating the anchor already set by the 
 \''\caption' command.
-- 
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