"Indic" glyph separation breaks mkmk

In the mark feature writer, marks belonging to Indic glyphs are placed in abvm/blwm features and other marks are positioned using mark/mkmk.

However… the Sharada script (which goes through the USE and is not considered “Indic” by ufo2ft) uses the Devanagari udatta (U+0951). When a Sharada font is compiled with ufo2ft, all the Sharada mark positioning rules go into mark/mkmk and the “Indic” rules (containing udatta) go into abvm. The glyphs are separated out into Indic/non-Indic before creating these rules, and this means there is no interaction between Sharada marks and Devanagari marks; i.e. there is no way to place a udatta on a Sharada mark such as a Candrabindu.

I don’t know if that’s linguistically something that you might want to do, but e.g. Noto Sans Sharada allows it, positioning all marks in the mkmk feature.

I don’t know how best to fix this:

• Add USE scripts to the indicScripts list?
• Provide a way of opting out of the abvm/blwm writer?

[simoncozens]

I’ll do a PR in a minute.

[anthrotype]

yes that one. Let’s add them all then