; grammar for ABNFs taken from RFC 5234 + RFC 7405,
; slightly adapted and extended to PEGs

rulelist       =  1*( rule / (*c-wsp c-nl) )

rule           =  rulename defined-as elements c-nl
                       ; continues if next line starts
                       ;  with white space

rulename       =  ALPHA *(ALPHA / DIGIT / "-")

defined-as     =  *c-wsp ("=/" / "=") *c-wsp
                       ; basic rules definition and
                       ;  incremental alternatives
                       ; different order due to PEG

elements       =  alternation *c-wsp

c-wsp          =  WSP / (c-nl WSP)

c-nl           =  comment / CRLF
                       ; comment or newline

comment        =  ";" *(WSP / VCHAR) CRLF

alternation    =  concatenation
                  *(*c-wsp "/" *c-wsp concatenation)

concatenation  =  predicate *(1*c-wsp predicate)

predicate      =  ["&" / "!"] repetition
                       ; extension for PEGs

repetition     =  [repeat] element

repeat         =  (*DIGIT "*" *DIGIT) / 1*DIGIT
                       ; different order due to PEG

element        =  rulename / group / option /
                  char-val / num-val / prose-val

group          =  "(" *c-wsp alternation *c-wsp ")"

option         =  "[" *c-wsp alternation *c-wsp "]"

char-val       =  DQUOTE *(%x20-21 / %x23-7E) DQUOTE
                       ; quoted string of SP and VCHAR
                       ;  without DQUOTE

num-val        =  "%" (bin-val / dec-val / hex-val)

bin-val        =  "b" 1*BIT
                  [ 1*("." 1*BIT) / ("-" 1*BIT) ]
                       ; series of concatenated bit values
                       ;  or single ONEOF range

dec-val        =  "d" 1*DIGIT
                  [ 1*("." 1*DIGIT) / ("-" 1*DIGIT) ]

hex-val        =  "x" 1*HEXDIG
                  [ 1*("." 1*HEXDIG) / ("-" 1*HEXDIG) ]

prose-val      =  "<" *(%x20-3D / %x3F-7E) ">"
                       ; bracketed string of SP and VCHAR
                       ;  without angles
                       ; prose description, to be used as
                       ;  last resort
