
So I'm making (not really designing per se) my own implementation of the American road sign fonts. I had an idea to implement arbitrary fractions, using superior and inferior digits and the fraction slash:

Then I have some kerning pairs between the digits and the fraction slash:

I export the font with both `kern` and `GPOS`-style kerning and the default OpenType script, but it doesn't really work:

There's really not much need for arbitrary fractions, so my users currently just use the pre-built composite fractions (¼½¾⅐⅑⅒⅓⅔⅕⅖⅗⅘⅙⅚⅛⅜⅝⅞). Still, they would love me so much if I made this work!

This is the font I am working on: Thanks in advance! ~Sammi
EDIT: The screenshot above is from this program: TrueType Viewer. I click the Features button to find the kern feature unchecked. Checking it makes the kerning work perfectly, but I assume this wouldn't work in other programs. Why is kerning optional?
