Regex Tester & Validator

This regex matches a sequence consisting of a digit between 1 and 3, followed by a digit between 4 and 6, and optionally the literal string 'nihao'. It is useful for validating or extracting short codes or identifiers that start with a number in the range 1-3, then a number in 4-6, and possibly a suffix like 'nihao'. Common use cases include parsing simple formatted tokens, filtering input patterns, or testing for specific numeric combinations with an optional keyword.