Your Go-To Regular Expression Reference: Hexadecimals

\x00 matches the NULL character, char code 0. \x01 matches SOH (start of heading), char code 1. \x02 matches STX (start of text), char code 2. \x03 matches ETX (end of text), char code 3. \x04 matches EOT (end of transmit), char code 4. \x05 matches ...