this may be a question that has an obvious answer. It came up in a discussion concerning the treatment of existing fonts: when you already have (manually) precomposed (Latin) glyphs in your font and extend the set of combining marks, what do you include in your ccmp feature according to best practice?
If there are precomposed marks for Vietnamese in your font, you will certainly want to include rules that invoke these precomposed marks as substitutes for sequences like /circumflexcomb/gravecomb/. Likewise, you may want to include contextual rules for caps-specific combining marks, if present, and for the glyphs /i/ and /j/ that will have to lose the dot before any diacritic can be added.
But beyond that? More specifically, does it make sense to add rules for precomposed glyphs such as /aacute/? In the sense that possible input sequences like /a/acutecomb/ will always result in the precombined glyph /aacute/ being used? Is that necessary?
Text shaping engines, I guess, are still defaulting to precombined glyphs if these glyphs are available in a font. So I would guess it is not necessary to add ccmp rules for glyphs like /aacute/, or is it?
Thank you for your insights,