BNF: Backus-Naur Form
There is a RFC 4234 for ABNF (Augmented BNF). No eBNF though.
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
BIT = "0" / "1"
CHAR = %x01-7F
; any 7-bit US-ASCII character,
; excluding NUL