I have a number of non-spacing marks that are not getting assigned any GDEF class. For example A674-A67D are all combining cyrillic non-spacing marks. They are properly defined as such in the internal GlyphData.xml. When I select these in the main window and choose Edit > Info for selection, I see that they have their category and subcategory correctly defined, but listed in gray. I check the boxes to “force” these values (or so I’d hoped) and the generated data still has no category assigned at all. We need this to work. Currently we have to post edit binary data to get the right GDEF.
Do they have anchors?
Ahh. They do not yet have anchors.
Hi Georg! I have been trying to get a Kannada problem to work for some time now, and it requires an “IgnoreMarks” lookup. Since I’m new to the program… can you explain a bit more about how GDEF is compiled by Glyphs? I want to make sure that my marks and base glyphs are correctly assigned. I created a custom GlyphData.xml file that assigned all of my non-unicode Kannada glyphs to either the “Letter” or “Marks” class, but it didn’t solve the problem. Do I need to add non-functioning anchors to the “Mark” glyphs in order for them to be automatically added to a “Marks” class that Glyphs compiles? Is there a way for me to manually define the GDEF classes? Thanks 
I understand. Could you send me your file and explain what you are trying to do?