ex.abnf

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

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  =  repetition *(1*c-wsp repetition)

repetition     =  [repeat] element

repeat         =  1*DIGIT / (*DIGIT "*" *DIGIT)

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
                      
ALPHA          =  %x41-5A / %x61-7A   ; A-Z / a-z

BIT            =  "0" / "1"

CHAR           =  %x01-7F
                      ; any 7-bit US-ASCII character,
                      ;  excluding NUL

CR             =  %x0D
                      ; carriage return

CRLF           =  CR LF
                      ; Internet standard newline

CTL            =  %x00-1F / %x7F
                      ; controls

DIGIT          =  %x30-39
                      ; 0-9

DQUOTE         =  %x22
                      ; " (Double Quote)

HEXDIG         =  DIGIT / "A" / "B" / "C" / "D" / "E" / "F"

HTAB           =  %x09
                      ; horizontal tab

LF             =  %x0A
                      ; linefeed

LWSP           =  *(WSP / CRLF WSP)
                      ; Use of this linear-white-space rule
                      ;  permits lines containing only white
                      ;  space that are no longer legal in
                      ;  mail headers and have caused
                      ;  interoperability problems in other
                      ;  contexts.
                      ; Do not use when defining mail
                      ;  headers and use with caution in
                      ;  other contexts.

OCTET          =  %x00-FF
                      ; 8 bits of data

SP             =  %x20

VCHAR          =  %x21-7E
                      ; visible (printing) characters

WSP            =  SP / HTAB
                      ; white space