After writing add-ons for like the past 8 years, I didn't realize that the first parameter of update callbacks of operator properties, conventionally named `self` is not actually what a Python coder would expect from a variable named `self`. I tried to document that here. This is in response to [what I thought was a bug](https://projects.blender.org/blender/blender/issues/110239). Pull Request: https://projects.blender.org/blender/blender/pulls/110242