This is very cool! If you put enter this regexp, you get a visualization of a Telnet protocol lexer. (?:[^\xFF\x0D]+|\x0D(?:\x0A|\x00)|\xFF(?:[\xFA\xFB\xFC\x

This is very cool! If you put enter this regexp, you get a visualization of a Telnet protocol lexer. (?:[^\xFF\x0D]+|\x0D(?:\x0A|\x00)|\xFF(?:[\xFA\xFB\xFC\xFD\xFE].|\xFF|.))* The graphic makes it obvious why Telnet requires NUL to follow any bare CR's: if it didn't, you would need a byte of lookahead!