> What is needed is a way to specify the properties in a > platform-independent way, where "platform" means not only "OS" but also > "font technology."
The font format used by all "smart font" technologies (OT, AAT, Graphite) are all based on the TrueType font file format which allows you to add any number of custom tables. If the people responsible for the OT, AAT & Graphite specs agreed on it amongst themselves, it might be possible to specify an embedded table of properties for PUA characters that all the different rendering engines could read and make use of. That might not be completely "font-technology independent" - but pretty close. - C