Running a bit short on space?

The other day in response to It's not right when IsRightToLeft is wrong, regular reader Andrew West asked in a comment after a brief conversation about the layout bits in the FONTSIGNATURE:

I know that the Unicode range bits are set in the OS/2 table of the font, but what about bits 123-125 -- are these also derived from the UnicodeRange field of the OS/2 table in the font?

A very good question, which I went ahead and asked some of the folks on the Microsoft Typography team who know this sort of thing (Sergey Malkin and Peter Constable).

The response from the two of them was that:

Bits 123+ are not defined in OS/2 Unicode ranges. And I think they can’t be there, because they are not font or font+script wide.

We have taken note to treat those bits as permanently reserved.

...we are getting close to the limit.... ...running out of bits (something like 10 left).

Clearly this is something to keep an eye on, since obviously there will be new scripts in Unicode, but to keep from needing to rev. the structure some new scripts will have to be combined with subranges that already exist.

So these three bits, while not specifically related to fonts themselves since fonts do not contain them, are reserved bits that fonts will not use.

This post brought to you by ? (U+a016, a.k.a. YI SYLLABLE BIT)