Hi,
I was asked to provide an alternative Arabic (Persian) glyph for zero for mathematical expression. Zero in most font faces is shaped as a rather large dot. This is confusing for its use in mathematical expression, in which, it is often used with a shape as a small O.
The question is not how to add the glyph, rather, what is the best way for an application to access it without activating a whole bunch of other 'alternative' glyphs?
I have a simple solution in AAT for that. But in OT I don't know how to go about it.

I was also thinking about adding some substitution scheme that is independent form applications. Such as zero+zwnj->zero.alt that could be encoded directly to get the mathematical zero. But I'm not sure how 'legal' this would be!