From: "Doug Ewell" <[EMAIL PROTECTED]> > Not all font formats, not even all "smart" font formats, can contain all > of the property information for every character the font supports. > OpenType/Uniscribe was mentioned as an example where the rendering > engine does work that would be done by the font in other systems. The > division of labor between font and engine isn't the same across systems. > And even if you can tell the font about the directionality and > default-ignorability of your characters, there are still issues like > line breaking and mirroring (and maybe others, or maybe those are bad > examples) that have to be handled outside the font anyway. > > Putting all the property information inside the font forces the user to > use *only that font* for his PUA needs. There might be a choice of > fonts that support a particular PUA usage (such as for Klingon -- Mark > Shoulson, is this true?) and it would not make sense to require all of > these fonts to be updated to include property information (if that is > even possible). Better to store the property information separately and > make it work for any old font the user chooses. > > Storing the custom properties in the font doesn't really provide any > assurance that they haven't been altered.
Still it seems legitimate to mark the font explicitly with the private convention it is supposed to support. For example a font containing glyphs mapped to PUAs assigned in the 2003 version of the ConScript PUA registry could be marked as such by including a trace of this private usage agreement. Without it, nothing will indicate explicitly in the font for which characters its internal PUA bindings were intented. A PUA signature URI (URL, tag URN, or UUID) added to that font could explicitly contain the trace of this agreement. I know that TrueType fonts for example contain language-specific features, marked with a internal language tag. If such PUA signature could be added as an optional attribute of a language tag, then the mechanism to embed this signature would be identical between: "participating" fonts, encoded plain text documents (using Unicode Language tags), XML/SGML/HTML documents (using language attributes of elements), and PUA definition XML files. May be AAT and Graphite or other fonts formats have a way to embed a standard language tag (by standard I mean a code which would work according to the RFC 3066 scheme or its successor, where optional attributes are encodable). > (Of course, all is not perfect > here -- we need to be careful to use U+100001 for our PUA examples, not > U+10001, which is an assigned Linear B character. Count your zeros > carefully!) I'm sorry to see that I didn't note the number of zeroes when replying to PUA usage examples. It's not important here, it was just an unnoticed typo that still makes sense as this was just a theorical example.
