augmented Backus Naur form (ABNF)

The constant advancement of description means led with the Backus Naur form( BNF) in the 90's to the Extended Backus Naur form (EBFN) and Augmented Backus Naur form (ABNF). The latter was further developed as a metalanguage for Internet technology and has its own syntax and derivation rules.

Augmented Backus Naur Form is compact, relatively simple and understandable. In the early years, the Arpanet had different ABNF definitions for e-mail, for example. In later documents, these definitions were separated to ensure consistent rules.

Unlike the classic Backus Naur Form (BFN), the augmented version introduced naming rules, repetitions, alternatives, and value ranges. It is described in RFC 4234.