draft-ietf-appsawg-mime-default-charset-03.txt   draft-ietf-appsawg-mime-default-charset-04.txt 
Applications Area Working Group A. Melnikov Applications Area Working Group A. Melnikov
Internet-Draft Isode Limited Internet-Draft Isode Limited
Updates: 2046 (if approved) J. Reschke Updates: 2046 (if approved) J. Reschke
Intended status: Standards Track greenbytes Intended status: Standards Track greenbytes
Expires: October 24, 2012 April 22, 2012 Expires: November 10, 2012 May 9, 2012
Update to MIME regarding Charset Parameter Handling in Update to MIME regarding Charset Parameter Handling in
Textual Media Types Textual Media Types
draft-ietf-appsawg-mime-default-charset-03 draft-ietf-appsawg-mime-default-charset-04
Abstract Abstract
This document changes RFC 2046 rules regarding default charset This document changes RFC 2046 rules regarding default charset
parameter values for text/* media types to better align with common parameter values for text/* media types to better align with common
usage by existing clients and servers. usage by existing clients and servers.
Editorial Note (To be removed by RFC Editor) Editorial Note (To be removed by RFC Editor)
Discussion of this draft should take place on the Apps Area Working Discussion of this draft should take place on the Apps Area Working
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 24, 2012. This Internet-Draft will expire on November 10, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . 3 1. Introduction and Overview . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . 3
3. New rules for default charset parameter values for 3. New rules for default charset parameter values for
text/* media types . . . . . . . . . . . . . . . . . . 3 text/* media types . . . . . . . . . . . . . . . . . . 3
4. Default charset parameter value for text/plain 4. Default charset parameter value for text/plain
media type . . . . . . . . . . . . . . . . . . . . . . 4 media type . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 5 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . 6
1. Introduction and Overview 1. Introduction and Overview
[RFC2046] specified that the default charset parameter (i.e. the RFC 2046 specified that the default charset parameter (i.e. the value
value used when it is not specified) is "US-ASCII". [RFC2616] used when the parameter is not specified) is "US-ASCII" (Section
changed the default for use by HTTP to be "ISO-8859-1". This 4.1.2 of [RFC2046]). RFC 2616 changed the default for use by HTTP
encoding is not very common for new text/* media types and a special (Hypertext Transfer Protocol) to be "ISO-8859-1" (Section 3.7.1 of
rule in HTTP adds confusion about which specification ([RFC2046] or [RFC2616]). This encoding is not very common for new text/* media
[RFC2616]) is authoritative in regards to the default charset for types and a special rule in the HTTP specification adds confusion
text/* media types. 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 Many complex text subtypes such as text/html [RFC2854] and text/xml
[RFC3023] have internal (to their format) means of describing the [RFC3023] have internal (to their format) means of describing the
charset. Many existing User Agents ignore the default of "US-ASCII" charset. Many existing User Agents ignore the default of "US-ASCII"
rule for at least text/html and text/xml. rule for at least text/html and text/xml.
This document changes RFC 2046 rules regarding default charset This document changes RFC 2046 rules regarding default charset
parameter values for text/* media types to better align with common parameter values for text/* media types to better align with common
usage by existing clients and servers. It does not change the usage by existing clients and servers. It does not change the
defaults for any currently registered media type. defaults for any currently registered media type.
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corresponding payloads (such as "text/html" and "text/xml") SHOULD corresponding payloads (such as "text/html" and "text/xml") SHOULD
NOT specify the use of a "charset" parameter, nor any default value, NOT specify the use of a "charset" parameter, nor any default value,
in order to avoid conflicting interpretations should the charset in order to avoid conflicting interpretations should the charset
parameter value and the value specified in the payload disagree. parameter value and the value specified in the payload disagree.
New subtypes of the "text" media type, thus, SHOULD NOT define a New subtypes of the "text" media type, thus, SHOULD NOT define a
default "charset" value. If there is a strong reason to do so default "charset" value. If there is a strong reason to do so
despite this advice, they SHOULD use the "UTF-8" [RFC3629] charset as despite this advice, they SHOULD use the "UTF-8" [RFC3629] charset as
the default. the default.
Regardless of what approach is chosen, all new text/* registrations
MUST clearly specify how the charset is determined; relying on the
default defined in Section 4.1.2 of [RFC2046] is no longer permitted.
However, existing text/* registrations that fail to specify how the
charset is determined still default to US-ASCII.
Specifications covering the "charset" parameter, and what default Specifications covering the "charset" parameter, and what default
value, if any, is used, are subtype-specific, NOT protocol-specific. value, if any, is used, are subtype-specific, NOT protocol-specific.
Protocols that use MIME, therefore, MUST NOT override default charset Protocols that use MIME, therefore, MUST NOT override default charset
values for "text/*" media types to be different for their specific values for "text/*" media types to be different for their specific
protocol. The protocol definitions MUST leave that to the subtype protocol. The protocol definitions MUST leave that to the subtype
definitions. definitions.
4. Default charset parameter value for text/plain media type 4. Default charset parameter value for text/plain media type
The default charset parameter value for text/plain is unchanged from The default charset parameter value for text/plain is unchanged from
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