Augmented BNF for Syntax Specifications: ABNF

原文：http://tools.ietf.org/html/rfc5234

Core Rules

Certain basic rules are in uppercase, such as SP,HTAB, CRLF, DIGIT,

   ALPHA, etc.

 

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

 

        BIT            =  "0" / "1"

 

        CHAR           = %x01-7F

                                ; any 7-bitUS-ASCII character,

                                ;  excluding NUL

 

 

 

         CR             = %x0D

                                ; carriagereturn

 

        CRLF           =  CR LF

                                ; Internet standardnewline

 

        CTL            =  %x00-1F / %x7F

                                ; controls

 

        DIGIT          =  %x30-39

                                ; 0-9

 

        DQUOTE         =  %x22

                                ; " (Double Quote)

 

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

 

        HTAB           =  %x09

                                ; horizontaltab

 

         LF             = %x0A

                                ; linefeed

 

        LWSP           =  *(WSP / CRLF WSP)

                                ; Use of thislinear-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 usewhen defining mail

                                ;  headers and use with caution in

                                ;  other contexts.

 

        OCTET          =  %x00-FF

                                ; 8 bits ofdata

 

         SP             = %x20

 

        VCHAR          = %x21-7E

                                ; visible(printing) characters

 

        WSP            =  SP / HTAB

                                ; white space