deprecate collecting kern classes from features.fea?

The KernFeatureWriter has a _collectFeaClasses that uses a regular expression to parse the features.fea text and collect all the @MMK_L_ and @MMK_R_ prefixed glyph classes. Apart from the problem that this doesn’t take into account include statements… why do that when UFO has groups.plist, where one can define public.kern1 and public.kern2 classes?

Do people actually use this feature? If so, why don’t they use groups.plist to store their kerning classes and instead write them as FEA classes?

I can’t remember the original purpose of this feature. Was it because some kerning tool (Metrics Machine?) used to do that?

I would like to simplify the API of the kern feature writer (before it actually gets more complex as we add more feature to it, e.g. dist, or refactoring RTL support), so I was thinking of dropping this.

[moyogo]

@anthrotype I think it’s fine to not collect even if there is a kern feature in the features file. UFOs should use the standard UFO kerning groups for simple kerning.

[anthrotype]

only UFO3 style kerning (public.kern1.* and public.kern2.* prefixes in groups.plist and kerning.plist) is now supported.