VoiceOver has some interesting undocumented heuristics with headings

I've noticed that in a pages document (tested only with document converted from word), VoiceOver in the vo-u rotor put under headings everything that seems to be in bold and/or have bigger font sizes, plus the actual heading style as defined in pages style formatter itself. The find next/previous headings only take into account the usual headings and they have their own separate issue as in larger document they are unpredictable. I'd have wished that apple provide better and clear documentation.