Here's what a regexp for a C-style identifier looks like (ranges are inclusive): [a-zA-Z_][a-zA-Z0-9_]* Here's what the same regexp would look like if reg

Here's what a regexp for a C-style identifier looks like (ranges are inclusive): [a-zA-Z_][a-zA-Z0-9_]* Here's what the same regexp would look like if regexp ranges were end-exclusive: [a-{A-[][a-{A-[0-:_]* Do you see the issue now? Of course if regexps really worked that way, you'd be better off doing this instead: [a-zzA-ZZ][a-zzA-ZZ0-99_] But that specific trick only works because regexp ranges occur in a set union context.