Here's the situation and I'm not sure if it can be done or if I'm just losing myself.
Given two base glyphs, I'd like to change the first one if the second has a combining mark. However, the first one can have 0-∞ combining mark.
Hence my problem. In this case I'd like to ignore combining marks on one part and ignore the base glyph on the second part, which would leave me with a simple "when X is followed by [list of combining marks], change to Y".
In regex it'd be
(B1)[`´¨]*B2[`´¨]+. Do I ask too much of OpenType?