Is Kern On deterministic?

[SCarewe]

Hello,

Since I am planning to work on a Cyrillic extension of a project, I was wondering what the implications are of using Kern On on a font that already is "finished" in its Latin state. In order to avoid text reflow and general changes to the existing font metrics/kerning, is it necessary to do the Cyrillic in a separate file? Or can I run KO again on the file (assuming I don't add any new models to the Cyrillic) and the kerning will be exactly the same?

Maybe more simply put: if I run KO on the same file twice, will the resulting kerning be exactly identical? Thank you!

[Tim Ahrens]

Yes, the result should be identical if you re-run Kern On. If it wasn’t then this would be a bug (but I do not think there is any potential for unintended side effects from additional glyphs in the font).