Is there any way to list/filter OT classes? If not, it would be cool if you could just type @classname like regular glyphs, and an entry in smart filters would be great.
An extra column in list view could be useful too. Right now, the only way to interact with OT classes is through the features panel, which is not much of course.
Also, how do I delete a custom list filter, the remove entry is grayed out?
Interesting idea. For now, that’s a good task for a script.
Cannot reproduce in app version 2.6.2 (1246). I select the list filter entry in the sidebar, click on the gear symbol in the corner and choose Remove Filter from the menu that pops up.
I’m on 1230. Both edit and remove filters from that menu are not available, I think it’s because I entered @classname in the list area … A filter with regular letters worked as expected, until I added % — then I couldn’t edit/remove it as well, even after generating /percent. Maybe it needs sanitizing?
Is there a way to remove them, it’s not a huge deal, but kind of annoying to have dummy filters there 
Try Script > Open Scripts Folder and in Finder, you will find a CustomFilter.plist next to your Scripts folder. You can open it in a plaintext editor like TextMate, Atom, BBEdit, Smultron, TextWrangler or SublimeText.
That worked. Testing with this file showed what I suspected — entering “(” without quotes breaks edit/remove, entering “parenleft” causes no trouble.
Thanks. Found the problem and fixed it.