[Devel] CFFs in SFNT problem

[Werner LEMBERG]

According to the CFF specs it is possible to have more than a single
font in a CFF (a `FontSet').[1] Is such a CFF possible if wrapped into
the SFNT format?

IMHO the answer is no.  The OT spec says (in cff.htm):

   Existing TrueType fonts use a glyph index to specify and access
   glyphs within a font, e.g. to index the loca table and thereby
   access glyph data in the glyf table.  This concept is retained in
   OpenType^TM PostScript fonts except that glyph data is accessed
   through the CharStrings INDEX of the CFF table.

This sentence makes only sense if there is a single CharStrings
index.  On the other hand, nothing in the OT spec prevents the
situation described above.  It looks like an omission.

I suggest to add the following sentence or something similar to the OT
spec:

  If there are multiple fonts in the CFF table (a `FontSet'), only the
  first font in the FontSet can be accessed.


     Werner


[1] I'm not talking about CID-keyed fonts which are collected in an
    FDArray -- it's easy to `flatten' such subfonts.