Regex Tester & Validator

This regex matches the prefix 'RSTART_' only when it is immediately followed by a sequence of exactly six uppercase alphanumeric characters (A-Z0-9) and then a digit, thanks to a lookahead assertion. It also matches the literal string 'NO_SIGNAL'. With the multiline flag, it can identify these markers across multiple lines. This is useful for detecting start-of-message signals or error states in log files, particularly in CAN bus or telemetry data streams.