[mpeg-OTspec] CFR ascender and descender

[Chapman, Christopher]

Hi Folks,

Ken and John, thanks for your responses to my question.

The word "typographic" was not so helpful a clue because the Microsoft typography webpage for the hhea table has:
FWORD	Ascender	Typographic ascent. (Distance from baseline of highest ascender)
FWORD	Descender	Typographic descent. (Distance from baseline of lowest descender)
[source: http://www.microsoft.com/typography/otspec/hhea.htm]

I checked 556 fonts that I had in my \Windows\Fonts directory and found that in 395 of them (i.e. about 71%) hhea.ascender and hhea.descender were not identical to OS/2.sTypoAscender and OS/2.sTypoDescender, so it seems that not all font tools follow the practice of making those attributes match.

I think it would be helpful to add some text to the CFR spec. clarifying from which OpenType font metrics a CFR should inherit its metrics if they are not explicitly specified in the CFR's XML, especially in the case of ascender and descender.  Thanks.

Cheers,
Christopher