[wrCisco]

Hi, since I didn't want to reappear just to point out that the plugin cssRemoveUnusedSelectors can be used to overcome some limitations of the builtin Delete Unused Stylesheet Classes, I took a peek at the Sigil source code to look for the culprit of this behavior.

If I correctly understood the code, Sigil in BookReports::AllClassesUsedInHTMLFileMapped retrieves all the couples tagname - classname used in xhtml files, and then look for a match with every css selector that happens to contain at least one .dot-preceded-classname (CSSInfo::getAllCSSSelectorsForElementClass). If the selector doesn't contain tagnames, it will match if it contains the appropriate classname, otherwise it will have to contain the appropriate sequence tagname.classname for the match to happen.

This is problematic for compound selectors, since they can contain tagnames and classnames which don't refer to the same element: so, if a user have a selector like ".chapter p" it will probably never match anything, and I'm afraid it won't be easy to amend the code (at least, it wouldn't be easy if it was me that had to work on it...).

A selector like "div.chapter p" will instead match if there is a div element in xhtml with the class chapter, even if it hasn't any p descendant - which can be good, I guess.

Pseudo classes and pseudo elements, like :first-of-type and ::first-line, seems to me that they aren't handled in any way in CSSInfo, so I suppose that they become part of the classname or the tagname that precedes them. In fact, if you have

<p class="matchthis:first-of-type">

in xhtml and

p.matchthis:first-of-type {}

in css, it won't be deleted.

(There is also the possibility that I misunderstood all the Sigil's source code and the answers are totally different. New year will tell... Cheers! )