Groups in (custom) list filters

[FlorianPircher]

This is not possible as far as I know. You can add custom headings in the glyphOder custom parameter like described here:

Organizing Glyphs Window

In the glyphOrder custom parameter, you can insert custom headings. Write a line that starts and ends with **, for example: **Letters, Latin** A B C **Swashes** _part.swash1 _part.swash2