How to listen for whether the option key is pressed in the right-click menu？

[FlorianPircher]

I am not quite shire what you are asking for. Maybe this is of help:

New API: Draw in Font View Glyph Cells

As of Glyphs 3.3 (3327), there is now an API for any plugin to draw in the foreground and background of glyph cells in Font View. This allows you to draw additional icons, background colors, or other decoration to indicate various aspects of the glyph or layer. For example, you can change the background color when the glyph has a certain tag. There is currently no Python wrapper, but you can use the Objective-C API from Python. A plugin registers an object (like self) to draw in the foreground …