What's wrong with regex? The trick is to break it down into components that you can read without a brain double panic. A little string catenation at run time won't hurt, I promise
Yeah, converting that to OG line numbered BASIC isn't happening anytime soon ๐
Edit: Actually, those regexps match up pretty closely to how I'd approach the problem in old BASIC, even if I didn't have anything like InStr or IndexOf and could examine a string only one character at a time in a For loop. It might look a bit like a state machine or DFA