Has this Plugin been updated, or is Glyphs 3 now able to show this?
The plug-in is available in the Plugin Manager, but it does not draw anything, correct.
In Console.app, it displays the error:
Traceback (most recent call last): File "/Users/mekka/Library/Application Support/Glyphs 3/Repositories/ShowUnderline/ShowUnderline.glyphsPlugin/Contents/Resources/plugin.py", line 40, in addUnderlineButton_ AttributeError: 'NSKVONotifying_GSEditViewController' object has no attribute 'userData'
Will have a look…
I fixed it.