Core.abnf

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