Decorate NSGlyphStorage to Replace Glyphs On-the-Fly
There are many ways to affect the glyphs that are used to show text on screen. Since macOS 10.11 El Capitan (released in 2015), possibly the simplest override points are in NSLayoutManagerDelegate. Another, arguably more ancient way to replace glyphs on-the-fly is to override and customize NSGlyphGenerator. This predates the existence of NSLayoutManagerDelegate, and it’s not even available on iOS, so that’s how arcane the approach outlines here will be.