V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

ABNF
       Augmented Backus-Naur Form (BNF, RFC 733/2234)


The Free On-line Dictionary of Computing (30 December 2018):

Augmented Backus-Naur Form
ABNF

    An extension of Backus-Naur Form documented in
   RFC 2234.

   [Summary?]

   (1997-11-23)