Might depend on your file browser.

You may also want to try, for example, the files “a1”, “a2”, “a3”, and “a10”. Lexicographically, “a2”>“a10”, but my file browser displays “a10” after “a2”.

Think the other way around: What’s the use case for case insensitive file names? Does it justify the effort and complexity for the filesystem and the programs to know the difference between lower and upper space chars?

Regular expressions in general, and automata theory, sure you should know about that. But a specific extended regex language like here? That’s like saying you’re shit at coding if you can’t do <insert arbitrary programming language here>.