附录 A. 汇总语法 (Collected Grammar)

本附录包含 RFC 2045 中定义的所有 MIME 语法规则的完整 BNF 语法.

这些 ABNF/BNF 片段是 MIME 头字段解析规则的一部分, 因此规则名、字面量、终结符和引用符号保持原文. 中文标题用于帮助读者定位语法区域, 不改变语法定义.

MIME 头字段

MIME-message-headers := entity-headers
                        fields
                        version CRLF

entity-headers := [ content CRLF ]
                  [ encoding CRLF ]
                  [ id CRLF ]
                  [ description CRLF ]
                  *( MIME-extension-field CRLF )

version := "MIME-Version" ":" 1*DIGIT "." 1*DIGIT

Content-Type

content := "Content-Type" ":" type "/" subtype
           *(";" parameter)

type := discrete-type / composite-type

discrete-type := "text" / "image" / "audio" / "video" /
                 "application" / extension-token

composite-type := "message" / "multipart" / extension-token

extension-token := ietf-token / x-token

ietf-token := <An extension token defined by a
               standards-track RFC and registered
               with IANA.>

x-token := <The two characters "X-" or "x-" followed, with
            no intervening white space, by any token>

subtype := extension-token / iana-token

iana-token := <A publicly-defined extension token.>

parameter := attribute "=" value

attribute := token

value := token / quoted-string

token := 1*<any (US-ASCII) CHAR except SPACE, CTLs,
            or tspecials>

tspecials :=  "(" / ")" / "<" / ">" / "@" /
              "," / ";" / ":" / "\" / <">
              "/" / "[" / "]" / "?" / "="

Content-Transfer-Encoding

encoding := "Content-Transfer-Encoding" ":" mechanism

mechanism := "7bit" / "8bit" / "binary" /
             "quoted-printable" / "base64" /
             ietf-token / x-token

Content-ID

id := "Content-ID" ":" msg-id

Content-Description

description := "Content-Description" ":" *text

---

说明:

• 此语法与 RFC 822 的 BNF 结合使用
• 一些规则引用 RFC 822 中定义的术语
• 完整语法需要参考 RFC 822 和 RFC 1123
• 实现解析器时应按语法规则处理大小写、特殊字符、quoted-string 和扩展 token, 不应翻译代码块中的任何符号