Dear Tomáš,
I suspected that the problem is due to exerquiz package.
Unfortunately yes, the problem can be removed by commenting out _all_
exerquiz stuff, then all error messages disappear.
I am afraid that exerquiz.4ht filter is old (as Michal already pointed
out) and needs to be updated. I have no idea how difficult it is,
please can someone have a look?
Attached is a tarball containing the LaTeX source file used for these
tests, the configuration file and all files required by the exerquiz
package.
Thanks for the sample file. It seems that the TeX4ht support file for
exerquiz is really old (it says 1999 in the literate sources!) and it
patches commands that are no longer part of this package.
I've found that it is better to remove all redefinitions from this file.
After that, there is only one problematic command. This command outputs
some postscript code at each chapter. It isn't really useful with
Tex4ht, so we can redefine it to do nothing. I can compile your file
without errors after this change.
I am not sure if the output looks good, especially the stuff that uses
exerquiz macros. I will try to look into this in the future. I am busy
with some work stuff at the moment unfortunately :/
Best regards,
Michal
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% exerquiz.4ht 2019-09-14-15:17 %
% Copyright (C) 1999-2009 Eitan M. Gurari %
% Copyright 2009-2019 TeX Users Group
%
% This work may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either
% version 1.3c of this license or (at your option) any
% later version. The latest version of this license is in
% http://www.latex-project.org/lppl.txt
% and version 1.3c or later is part of all distributions
% of LaTeX version 2005/12/01 or later.
%
% This work has the LPPL maintenance status "maintained".
%
% The Current Maintainer of this work
% is the TeX4ht Project <http://tug.org/tex4ht>.
%
% If you modify this program, changing the
% version identification would be appreciated.
\def\headerps@out#1{}
