I'm checking the kerning of an OT font that I thought was close to finished. Everything looked to be working well in Illustrator and InDesign except the OX and ox combination don't kern. XO and xo combinations kern in. But OX and ox don't. I just realized the same thing happens with the small caps.
I can't figure out why. The OT features compile no problem. The Kerning Assistance Tool finds no errors. It all looks good in the Metrics windows. All the OAO, OVO and OYO combinations work properly. The X glyphs are just about the only glyphs not part of any kerning class in this font. The O is part of the C class on the left and the D class on the right. The o is part of the c class on the left and the b class on the right.
I'm not sure what to do to fix it. Does it make sense to put the X into a class by itself? With just the one glyph in the class?