Let’s say we have a font with tabular lining figures as the default (i.e. mapped to Unicode values). If the fonts has the pnum and onum feature that would allow to access all four figure styles (assuming there are four sets). Why woud we include tnum or lnum? They should not have any use or effect.
Theoretically, a user my have chosen figures from InDesign’s glyph palette so tnum or lnum could indeed have an effect but that’s unlikely. Another argument I can imagine is that the OT features of a font may turn up in some kind of shop situation (third-party distributor) and potential buyers who are not so technically savvy may think the font is not fully featured if tnum and lnum are “missing”. Or, are there UIs that simply rely on the presence of all four features?
Another argument would be that people already have documents/websites/interfaces that do not assume the tabular lining are on default and they would like to, or rather, they already have set up a way to access it via those features.
So, while this is correct and the behaviour is as expected, I can see reasons to include pnum and onum (which could probably even be empty) to “enable” the Porportional Oldstyle menu entry.
Not sure I understand what you mean. Access what via which features? If a feature is activated that is not present in the font then this should be ignore so you would still get the desired result.
It is like you say. If the feature is not present it is ignored.
But the solution you propose doesn’t guarantee that, if one the features (for example onum) is not present, then i can find it in the default figure style. That alone only adds to what is already confusing for some.
