Aalt export warning that looks correct

On checking my export log I see:

feature ‘frac’, referenced in aalt feature, either is not defined or had no rules which could be included in the aalt feature.

However, I do have a frac feature which is auto generated. The feature seems to work fine, so is the error symptomatic of something else?

You can ignore this.

It is about aalt, which should only reference simple one-to-one substitutions. frac is probably contextual though, and then it will be ignored by makeotf, that’s all. Nothing to worry about.

Thanks. That all makes sense.