[KevinH]

Yes, it is how Sigil notes which headings to not add to the TOC when generating it. This is how Sigil has always marked such entries during creation of a TOC from the very beginning of Sigil.

You can of course remove them after your your TOC is in final form if you want but if you change your mind you may have to again add your limit to which headings to include or not.

They are also useful when exceptions are made when editing the TOC ie. using Edit TOC and deleting an entry. When doing that, you do not want to actually delete a heading from the actual xhtml, you just want to mark it so that it is ignored when building the TOC itself.

FYI - Sigil also adds ids to headings when creating or making subheadings and detecting when changes are made.

They will not hurt anything (they are a marker class) but can be useful for styling unused headings. I add CSS to make them standout (colour red) so I can find them when editing. Sometimes I use the css to mark them as hidden.

The concept of using marker classes is quite common in javascript to allow fast selection of elements. Similar things can be done using id attributes.

If you are absolutely sure everything TOC related is final (no new files, no new headings, no heading wording changes) and you do not want to style unused headings as hidden (or greyed out, or make them visually distinct for editing), you can of course run a search and replace to remove them or use them to remove entire unused headings.

I just leave them in since they are a good way to mark headings that are unused. Note, that marking for index generation also uses marker classes.