TYPO3 Core

I know what transformations do and I know when and how to use exit/entryHTMLparser. But when I have to use HTMLparser_db/rte?

Following don't works
HTMLparser_db.tags.h1.fixAttrib.class.set = newClassName

Following works
HTMLparser_db.tags.b.remap = i

Following works, too
exitHTMLparser_db.tags.h1.fixAttrib.class.set = newClassName

So when HTMLparser_db was executed. Before or after the transformation?

In documentation for HTMLparser_db I found following information:

.nestingGlobal for HTMLparser_db is set by default to “b,i,u,a,center,font,sub,sup,strong,em,strike,span” unless another value is set.

But there is no such property. I only find: .globalNesting
(issue imported from #M12711)