Nice article, it’s usually hard to keep a reader’s interest when writing about shell. I will nitpick that COMP_LINE et al are shell variables, not environment

Nice article, it’s usually hard to keep a reader’s interest when writing about shell. I will nitpick that COMP_LINE et al are shell variables, not environment variables - you can tell by the fact you don’t need to export the “return value”. (Scare quotes, as the function’s exit code, manually specifiable with “return NN”, is also called its return value.)