Internet Engineering Task Force (IETF) A. Melnikov
Request for Comments: 6657 Isode Limited
Updates: 2046 J. Reschke
Category: Standards Track greenbytes
ISSN: 2070-1721 July 2012
Update to MIME regarding "charset" Parameter Handling
in Textual Media Types
Abstract
This document changes RFC 2046 rules regarding default "charset"
parameter values for "text/*" media types to better align with common
usage by existing clients and servers.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6657.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Melnikov & Reschke Standards Track [Page 1]RFC 6657 MIME Charset Default Update July 2012Table of Contents
1. Introduction and Overview .......................................2
2. Conventions Used in This Document ...............................2
3. New Rules for Default "charset" Parameter Values for
"text/*" Media Types ............................................3
4. Default "charset" Parameter Value for "text/plain" Media Type ...4
5. Security Considerations .........................................4
6. IANA Considerations .............................................4
7. References ......................................................4
7.1. Normative References .......................................4
7.2. Informative References .....................................5
Appendix A. Acknowledgements ......................................6
1. Introduction and Overview
RFC 2046 specified that the default "charset" parameter (i.e., the
value used when the parameter is not specified) is "US-ASCII"
(Section 4.1.2 of [RFC2046]). RFC 2616 changed the default for use
by HTTP (Hypertext Transfer Protocol) to be "ISO-8859-1" (Section
3.7.1 of [RFC2616]). This encoding is not very common for new
"text/*" media types and a special rule in the HTTP specification
adds confusion about which specification ([RFC2046] or [RFC2616]) is
authoritative in regards to the default charset for "text/*" media
types.
Many complex text subtypes such as "text/html" [RFC2854] and "text/
xml" [RFC3023] have internal (to their format) means of describing
the charset. Many existing User Agents ignore the default of "US-
ASCII" rule for at least "text/html" and "text/xml".
This document changes RFC 2046 rules regarding default "charset"
parameter values for "text/*" media types to better align with common
usage by existing clients and servers. It does not change the
defaults for any currently registered media type.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Melnikov & Reschke Standards Track [Page 2]RFC 6657 MIME Charset Default Update July 2012
3. New Rules for Default "charset" Parameter Values for "text/*" Media
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