Unimplement[ed,able] spots in the OpenType spec

This Twitter thread from earlier in the week (about the Component class in GDEF, and whether it really is used) started me thinking — there are a number of elements in the OpenType specification that are pretty widely recognized as being "not practically implementable" for one reason or another, such as lack of detail or, perhaps, because they were a little aspirational when they were first added, and things went a different direction....

For example, the JSTF table or the `rand` feature. But they tend to emerge in discussions rather arbitrarily & unpredictably when someone bumps into them.

So I wonder: is there a somewhat-current list somewhere of those bits & gaps? The things that are listed in the spec, but cannot actually be supported IRL? Other than digging through HarfBuzz source code or font-editor documentation, that is.

Or, if there's not such a list, then alternatively please feel free to chime in with replies and perhaps have a casual one emerge below....

(I do realize that there's a lot of personal interpretation in calling something "impractical" or "not implementable"; I'm totally fine with those caveats being assumed and nobody will take such a comment as being official or definitive. Unless you want to make a case for yours.)

Comments

  • Simon CozensSimon Cozens Posts: 625
    In terms of OpenType features, if I were having a clean out of the ones that never really made it, I'd get rid of falt, hang, opbd, ltbd/rtbd, smpl, tnam, valt, and vrt2.
  • Nathan WillisNathan Willis Posts: 10
    In terms of OpenType features, if I were having a clean out of the ones that never really made it, I'd get rid of falt, hang, opbd, ltbd/rtbd, smpl, tnam, valt, and vrt2.

    Do you mean `hngl` there?
  • Simon CozensSimon Cozens Posts: 625
    Yes.
  • John HudsonJohn Hudson Posts: 2,443
    In terms of OpenType features, if I were having a clean out of the ones that never really made it, I'd get rid of falt, hang, opbd, ltbd/rtbd, smpl, tnam, valt, and vrt2.
    Don’t forget ‘size’. Probably the most batshit conceptual feature.
  • Erwin DenissenErwin Denissen Posts: 271
    Don’t forget ‘size’. Probably the most batshit conceptual feature.
    Sort of related is OS/2 version 5, as that added two fields (usLowerOpticalPointSize and usUpperOpticalPointSize) that are now superseded by the STAT table.
  • John HudsonJohn Hudson Posts: 2,443
    Correct. The OS/2 v5 size fields were under-specified in that they did not provide for complex family mappings. They could have been made to work, with some name table additions, but STAT is a better mechanism.
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