Augmented BNF for Syntax Specifications: ABNF
ABNF
Augmented
Backus-Naur
Form
electronic
mail
In the early days of the Arpanet, each specification contained its own definition of ABNF. This included the email specifications, RFC733 and then RFC822 which have come to be the common citations for defining ABNF. The current document separates out that definition, to permit selective reference. Predictably, it also provides some modifications and enhancements. [STANDARDS-TRACK]