Per post by Michal at https://tex.stackexchange.com/questions/631604/how-to-split-an-article-at-the-subsubsection-level-using-tex4ht
-------------------- For document classes with \chapter command: 1 - split at \part 2 - split at \chapter 3 - split at \section 4 - split at \subsection 5 - split at \subsubsection 6 - split at \paragraph You stopped trying numbers too early. The numbers seem to work like this: For document classes with \chapter command: 1 - split at \part 2 - split at \chapter 3 - split at \section 4 - split at \subsection 5 - split at \subsubsection 6 - split at \paragraph For document classes without \chapter (like article): 1 - split at \part 2 - split at \section 3 - split at \subsection 5 - split at \subsubsection 6 - split at \paragraph ----------------------------------------- My question is: Why does in article, it skips split level 4, and goes from 3 to 5? I find this confusing. May be there is reason internally when tex4ht does this? I'd like to suggest for some future version that this option should be redone. May be add new option calling it "split_at" so current method stays backward compatible. The new option will have the form split_at="name" where name can be "part" or "chapter" or "section" or "subsection" and so on. So one can now do make4ht foo.tex 'html,mathjax,split_at="section"' If string does not work for value, it can just name, as in make4ht foo.tex 'html,mathjax,split_at=section' Not only is this much more clear than make4ht foo.tex 'html,mathjax,3' But with the new option, one do not have to worry changing the command to get the numbers right, if they change from article to book. It is also much more clear looking at the command, where the split will happen, since it is a name and not a magic number. Thank you, --Nasser