There are about 140 OpenType layout features listed on https://docs.microsoft.com/en-us/typography/opentype/spec/featurelist
. Should all of these be offered to an end user, specifically a web developer setting type with CSS? Or should some features be left out of a possible UI or out of a CSS font-feature-settings declaration? Is there a list of layout features that should be configured by a user of the font?
And, as a related question, I noticed the phenomenon of layout features seemingly cancelling others out. For example, I enable frac and the text "1/2 beers" turns into "½ beers". Then I also
turn on smcp, and for some fonts, instead of getting "½ BEERS" I get "1/2 BEERS". With other fonts, it'll work as expected. All the fonts I tested do have frac and smcp.
I think this might have to do with the order lookups happen in, and that each substitution can only happen once. I remember reading about this but can't find the discussion any more.
Something like this would be confusing to the end user, so how are you supposed to deal with that? "When combining layout features, some features can magically disappear even though you turned them on" sounds like a bad disclaimer for a font settings UI/tool.
(I'm aware I might be missing something super obvious, so if there's any reading I should catch up on first, please let me know.)