Cldr.Number.Format.Compiler.number_match_regex

You're seeing just the function number_match_regex, go back to Cldr.Number.Format.Compiler module for more information.

A regular expression that can be used to split either a number format or a number itself.

Since it accepts characters that are not digits (like '#', '@' and ',') it cannot be used to validate a number. Its only use is to split a number or a format into parts for later processing.