Hi! It would be great, if Predefined Sorting could have customizable categories. Sometimes default sorting isn’t perfect, especially for rare glyphs, so I stick with glyphOrder property, but missing the categories. Not a top-of-the-list kind of request, but would be nice to have it at some point.
Or is there a way to customize categories/ordering without the property?
There are some better options coming in a future version.
For now your best option is to tweak the sortName property of your glyphs by setting up custom glyph data for the glyphs that need different sorting: https://glyphsapp.com/tutorials/roll-your-own-glyph-data
Or, you tell me what bothers you and I might fix it in Glyphs directly.
When we wanted to have a custom sorting for our fonts with categories (which add a lot of clarity to navigate big glyph sets), we resorted to making a custom GlyphData file.
It would be great though if sorting and “categorizing” of glyphs could be dealt with in a separated way from encoding and other settings that GlyphData handles. My guess is a lot of people might want to sort their glyphs and use custom categories but are perfectly happy with Glyphs’ default behavior regarding encoding, anchors settings, composites etc… so having to edit GlyphData maybe is a bit overkill for doing just that?
As I said, improvements are coming.
@GeorgSeifert can we expect Glyphs 3 in 2020? 
Glyphnado 3, Global Kerning
Hi. Can I ask if there is now a better way to define sorting other than the glyphOrder custom parameter?
You can set the glyph.sortName to sort inside the existing groups. Other than that, only the glyphOrder parameter.