Regex Tester & Validator

This regex matches usernames that must begin with either an underscore or a period, followed by one or more digits, then optional letters, and an optional trailing underscore. It enforces a specific naming convention where the first character is a punctuation mark, and the rest is alphanumeric with a possible underscore at the end. Common use cases include validating form inputs, generating unique identifiers, or filtering usernames in systems that require a numeric component.