RFC 2231 Proposed Standard Message format

MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations

This memo defines extensions to the RFC 2045 media type and RFC 2183 disposition parameter value mechanisms. This memo also defines an extension to the encoded words defined in RFC 2047 to allow the specification of the language to be used for display as well as the character set. [STANDARDS-TRACK]

Status
Proposed Standard. On the standards track and stable enough to implement against. Most of the email stack stays at this level permanently.
Published
November 1997
Authors
N. Freed, K. Moore
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Replaces RFC 2184: MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations.

Normative requirements

Every sentence in this RFC carrying an RFC 2119 keyword, with the section it came from. 8 must, 2 should, 0 may.

2.1 Requirements notation

  • MUSTWhen the terms "MUST", "SHOULD", "MUST NOT", "SHOULD NOT", and "MAY" appear capitalized, they are being used to indicate particular requirements of this specification.

3 Parameter Value Continuations

  • MUSTAny such mechanism MUST be compatible with existing MIME processors.
  • MUST NOT(1) the mechanism MUST NOT change the syntax of MIME media type and disposition lines, and
  • MUST NOT(2) the mechanism MUST NOT depend on parameter ordering since MIME states that parameters are not order sensitive.

4 Parameter Value Character Set and Language Information

  • MUSTNote also that the single quote delimiters MUST be present even when one of the field values is omitted.
  • MUST NOTThis MUST NOT be done in order to indicate a default character set or language -- parameter field definitions MUST NOT assign a default character set or language.

4.1 Combining Character Set, Language, and Parameter Continuations

  • MUST(4) The first segment of a continuation MUST be encoded if language and character set information are given.
  • MUST(5) If the first segment of a continued parameter value is encoded the language and character set field delimiters MUST be present even when the fields are left blank.

6 IMAP4 Handling of Parameter Values

  • SHOULDIMAP4 [RFC-2060] servers SHOULD decode parameter value continuations when generating the BODY and BODYSTRUCTURE fetch attributes.

8 Character sets which allow specification of language

  • SHOULDIf and when such facilities are developed they SHOULD be used in preference to the language labeling facilities specified here.

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