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