Any way to create new categories and subcategories?

Just like the subject says, I’m wondering if there’s a way to create new categories and subcategories. Would be similar to Custom Filters, but sorted with the other categories, and based on a list of glyphs rather than some dynamic criteria. Possible?

I guess what you need is a list filter, not new categories. List filter is a list of glyphs that you want. Make a new one from the bottom left just like you would make a new custom filter, and list all glyphs you want, one letter per line.

Oh man, I had no idea that was even a thing. Embarrassing. Thanks!