bug#50177: Support U+20DD COMBINING ENCLOSING CIRCLE

[Werner LEMBERG]

>> CC'ing Handa-san, in the hope that he could explain better why we
>> disallow character composition from different fonts.
> 
> The main reason is what Eli wrote. An opentype font contains rules
> to tell how to compose two glyphs in that font.  But such rules are
> specific to that font, and there's no way to combine rules of
> different fonts.  So, an opentype rendering engine does not work for
> different fonts.
> 
> And, when we artificially compose characters from different fonts,
> there is a possibility that the resulting image looks like a
> different character which I think is worse than not composing.

+1


    Werner