epubcheck with error

Question

Now I am trying to validate produced epub files with the programm epubcheck, which I installed correctly and already used successfully to other newly produced epub files with tex4ebook.

But now I got an error message (or 9 nearly identical ones) when validating a larger epub file (with toc and indexing).

The error message is in german an says:

filename.epub/pathnameli1.html(12,38): Validierungsfehler: Der Wert des Attributs "id" ist ungültig; es muss ein XML-Name ohne Doppelpunkte sein

Translated:

filename.epub/pathnameli1.html(12,38): validation error: the value of attribute "id" is not valid; it needs to be a XML-name without colon.

I got this for pathnameli3.html, pathnameli5.html,..., pathnameli17.html. As a whole "9 errors".

When I open pathnameli3.html I find the following line refering to "id":

...
 <h2 class='likechapterHead' id='1'><a id='x5-3000'></a></h2>
...

Concerning the filename.tex source it refers obviously to the first pages with toc. Up to now I could not reproduce the error in a MWE. Maybe someone can get some hints out of this. What might be wrong? How to validate the epub up to "0 error"?

Edit 1

I looked at the pathnameli1.html (which produces an error), pathnameli2.html (which does not produce an error).

I find that the odd numbers up to 17 produce 9 errors messages of the above kind. The even numbers (2, 4, 6, 8, 10, 12, 14, 16) are as follows:

2: <h2 class='likechapterHead' id='vorwort'><a id='x3-2000'></a>Vorwort</h2>

They even numbers represent the all the \chapter*{} commands of the document.tex

Then I looked at these chapter commands in the document.tex and found \cleartooddpage commands and thought that it has to do with the problem and changed it to \clearpage. But the errors remained.

I do not understand the odd numbers of the pathnameli1.html and so on. Where are they produced in the document.tex? But they do come eventually with tex4ebook?

The part of relevant document.tex is as follows:

\cleartooddpage
\chapter*{Vorwort}
\ifdefined\HCode
\else\phantomsection\addcontentsline{toc}{chapter}{Vorwort}
\fi
\pagenumbering{arabic}
\thispagestyle{empty}
\pagestyle{Vorwort}

Edit 2 - Full example

This is the full example:

\documentclass[11pt,a4paper]{report}
\usepackage{ebgaramond-maths}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{fancyhdr}
\usepackage{nextpage}
\usepackage{tex4ebook}
\providecommand\phantomsection{}
\ifdefined\HCode
\usepackage[xindy,noautomatic]{imakeidx}
\else
\usepackage[]{imakeidx}
\fi
\makeindex[intoc=false,columns=1,noautomatic,title=Alphabetisches Verzeichnis]
\ifdefined\HCode
\usepackage[hyperindex=true,
pdfauthor={Autor},
pdftitle={Titel},
pdfkeywords={Keyword}]{hyperref}
\else\fi
\fancypagestyle{Inhaltsverzeichnis}{\fancyhf{}%
    \fancyhead[RO,LE]{\small\rmfamily\thepage}
    \fancyhead[LO,RE]{\small\scshape Inhaltsverzeichnis}}   
\fancypagestyle{Vorwort}{\fancyhf{}%
    \fancyhead[RO,LE]{\small\rmfamily\thepage}
    \fancyhead[LO,RE]{\small\scshape Vorwort}}
\fancypagestyle{Something}{\fancyhf{}%
    \fancyhead[RO,LE]{\small\rmfamily\thepage}
    \fancyhead[LO,RE]{\small\scshape About Something}}
\fancypagestyle{AlphabetischesVerzeichnis}{\fancyhf{}%
    \fancyhead[RO,LE]{\small\rmfamily\thepage}
    \fancyhead[LO,RE]{\small\scshape Alphabetisches Verzeichnis}}   
\usepackage{titletoc}
\titlecontents{chapter}[2pc]%
{\addvspace{0.5pc}\normalsize\scshape}%
{\contentslabel{2pc}}%
{\contentslabel{2pc}}{, \thecontentspage}%
[]
\titlecontents{section}[2pc]%
{\addvspace{0.1pc}\small\rmfamily}%
{\contentslabel{2pc}}%
{\contentslabel{2pc}}{, \thecontentspage}%
[]
\usepackage[rm,sc,small,center]{titlesec}
\renewcommand{\thechapter}{}
\titleformat{\chapter}[display]%
{\Huge\scshape}%
{}%
{0pt}{\filcenter}%
[]
\renewcommand{\thesection}{\arabic{section}}
\titleformat{\section}[display]%
{\large\scshape}%
{\filcenter\normalsize\textbf{\thesection}}%
{0pt}{\filcenter}%
[]

\begin{document}
\pagenumbering{roman}
\pagestyle{empty}

\ifdefined\HCode
\phantomsection
\addcontentsline{toc}{chapter}{Cover}
\coverimage[natwidth=\paperwidth,natheight=\paperheight]{Cover_Someimage.jpg}
\fi
\clearpage
\normalsize
... Some pages with empty pagestyle ...

\cleartooddpage
\begingroup
\makeatletter
\ifdefined\HCode
\else
\phantomsection
\addcontentsline{toc}{chapter}{Inhaltsverzeichnis}
\let\ps@plain\ps@empty
\pagestyle{Inhaltsverzeichnis}
\tableofcontents
\fi
\clearpage
\endgroup

\cleartooddpage
\chapter*{Vorwort}
\ifdefined\HCode
\else\phantomsection\addcontentsline{toc}{chapter}{Vorwort}
\fi
\pagenumbering{arabic}
\thispagestyle{empty}
\pagestyle{Vorwort}
... Some Foreword ...

\cleartooddpage
\chapter*{About Something}
\ifdefined\HCode
\else\phantomsection\addcontentsline{toc}{chapter}{About Something}
\fi
\thispagestyle{empty}
\pagestyle{Something}
\clearpage
\section{First}\index{First}
... Some first things...
\clearpage
\section{Second}\index{Second}
... Some second things....

\cleartooddpage
\begingroup
\makeatletter
\let\ps@plain\ps@empty
\pagestyle{AlphabetischesVerzeichnis}
\label{AlphabetischesVerzeichnis}
\small
\renewcommand{\indexname}{\Large Alphabetisches Verzeichnis}
\phantomsection\addcontentsline{toc}{chapter}{Alphabetisches Verzeichnis}
\printindex
\clearpage
\endgroup
\end{document}

It reproduces the error 3 times. And also with the odd numbers pathnameli1.html for 1, 3, 5.

Answer 1

This seems to be caused by titlesec, it inserts spurious empty chapter, which produces extra page. This can be fixed using this file, titlesec-hooks.4ht:

% titlesec-hooks.4ht (2022-03-16-14:13), generated from tex4ht-4ht.tex
% Copyright 2022 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.
\immediate\write-1{version 2022-03-16-14:13}

\let\ttl:@makechapterhead\@makechapterhead
\let\ttl:@makeschapterhead\@makeschapterhead
\let\ttl:chapter\chapter
\let\ttl:section\section
\let\ttl:subsection\subsection
\let\ttl:subsubsection\subsubsection
\let\ttl:paragraph\paragraph
\let\ttl:subparagraph\subparagraph
\:AtEndOfPackage{
  \let\chapter\ttl:chapter
  \let\section\ttl:section
  \let\subsection\ttl:subsection
  \let\subsubsection\ttl:subsubsection
  \let\paragraph\ttl:paragraph
  \let\subparagraph\ttl:subparagraph
  \let\@makechapterhead\ttl:@makechapterhead
  \let\@makeschapterhead\ttl:@makeschapterhead
  \def\ttl@format@si#1#2#3#4#5#6#7{}
  \def\ttl@format@ii#1[#2]#3#4#5#6{
    \@ifnextchar[{%
      \ttl@format@iii{#2}%
    }{%
      \ttl@format@iii{#2}[]}
  }
  \def\ttl@format@iii#1[#2]{}
}

\endinput

It cancels the redefinition of the \@makeschapterhead command, to prevent any stuff that titlesec does to it.