Regex Tester & Validator

This regex matches US Alien Registration Numbers (A-numbers) in two common formats: either three letters followed by ten digits (e.g., ABC1234567890), or three letters followed by space-separated groups of two, three, and five digits (e.g., ABC 12 345 67890). It is useful for extracting or validating immigration document identifiers from text, with multiline support to find matches across multiple lines.