Network Working Group G. Klyne
Request for Comments: 2913 Content Technologies
Category: Standards Track September 2000
Network Working Group G. Klyne
Request for Comments: 2913 Content Technologies
Category: Standards Track September 2000
MIME Content Types in Media Feature Expressions
媒体功能表达式中的MIME内容类型
Status of this Memo
本备忘录的状况
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
本文件规定了互联网社区的互联网标准跟踪协议，并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态，请参考当前版本的“互联网官方协议标准”（STD 1）。本备忘录的分发不受限制。
Copyright Notice
版权公告
Copyright (C) The Internet Society (2000). All Rights Reserved.
版权所有（C）互联网协会（2000年）。版权所有。
Abstract
摘要
In "A Syntax for Describing Media Feature Sets", an expression format is presented for describing media feature capabilities using simple media feature tags.
在“描述媒体功能集的语法”中，提供了一种表达式格式，用于使用简单的媒体功能标签描述媒体功能。
This memo defines a media feature tag whose value is a Multipurpose Internet Mail Extensions (MIME) content type. This allows the construction of feature expressions that take account of the MIME content type of the corresponding data.
此备忘录定义了一个媒体功能标签，其值为多用途Internet邮件扩展（MIME）内容类型。这允许构造考虑相应数据的MIME内容类型的功能表达式。
Table of Contents
目录
1. Introduction .................................................. 2
1.1 Terminology and document conventions ...................... 2
2. Motivation and goals .......................................... 3
3. MIME content type feature tag ................................. 3
4. Examples ...................................................... 4
4.1 Simple text ............................................... 4
4.2 Fax image ................................................. 4
4.3 Voice message ............................................. 4
4.4 Web browser capabilities .................................. 5
5. IANA Considerations ........................................... 5
6. Security Considerations ....................................... 5
7. Acknowledgements .............................................. 5
8. References .................................................... 6
9. Author's Address .............................................. 6
Appendix A: 'Type' feature tag registration ...................... 7
Full Copyright Statement ......................................... 9
1. Introduction .................................................. 2
1.1 Terminology and document conventions ...................... 2
2. Motivation and goals .......................................... 3
3. MIME content type feature tag ................................. 3
4. Examples ...................................................... 4
4.1 Simple text ............................................... 4
4.2 Fax image ................................................. 4
4.3 Voice message ............................................. 4
4.4 Web browser capabilities .................................. 5
5. IANA Considerations ........................................... 5
6. Security Considerations ....................................... 5
7. Acknowledgements .............................................. 5
8. References .................................................... 6
9. Author's Address .............................................. 6
Appendix A: 'Type' feature tag registration ...................... 7
Full Copyright Statement ......................................... 9
In "A Syntax for Describing Media Feature Sets" [1], an expression format is presented for describing media feature capabilities as a combination of simple media feature tags, registered according to "Media Feature Tag Registration Procedure" [2]. This provides a format for message handling agents to describe the media feature content of messages that they can handle.
在“描述媒体功能集的语法”[1]中，提供了一种表达式格式，用于将媒体功能功能描述为简单媒体功能标签的组合，并根据“媒体功能标签注册程序”[2]注册。这为消息处理代理提供了一种格式，用于描述它们可以处理的消息的媒体功能内容。
This memo defines a media feature tag whose value is a MIME content type. This allows the construction of feature expressions that take account of the MIME content type of the corresponding data.
此备忘录定义了一个媒体功能标签，其值为MIME内容类型。这允许构造考虑相应数据的MIME内容类型的功能表达式。
Note that a content type feature value may contain parameters, but this is discouraged. See section 3 and appendix A, "Summary of the media features indicated" for discussion of this point.
请注意，内容类型要素值可能包含参数，但不建议这样做。有关这一点的讨论，请参见第3节和附录A“所示媒体功能的总结”。
This section defines a number of terms and other document conventions, which are used with specific meaning in this memo.
本节定义了许多术语和其他文件惯例，这些术语和惯例在本备忘录中具有特定含义。
media feature information that indicates facilities assumed to be available for the message content to be properly rendered or otherwise presented. Media features are not intended to include information that affects message transmission.
媒体功能信息，指示假定可用于正确呈现或以其他方式呈现消息内容的设施。媒体功能不包括影响消息传输的信息。
feature set some set of media features described by a media feature assertion, as described in "A Syntax for Describing Media Feature Sets" [1]. (See that memo for a more formal definition of this term.)
功能集由媒体功能断言描述的一些媒体功能集，如“描述媒体功能集的语法”[1]中所述。（有关该术语更正式的定义，请参见该备忘录。）
feature set expression a string that describes some feature set, formulated according to the rules in "A Syntax for Describing Media Feature Sets" [1] (and possibly extended by other specifications).
功能集表达式描述某些功能集的字符串，根据“描述媒体功能集的语法”[1]中的规则制定（可能由其他规范扩展）。
This specification uses syntax notation and conventions described in RFC 2234, "Augmented BNF for Syntax Specifications: ABNF" [3].
本规范使用RFC 2234“语法规范的扩充BNF:ABNF”[3]中描述的语法符号和约定。
NOTE: Comments like this provide additional nonessential information about the rationale behind this document. Such information is not needed for building a conformant implementation, but may help those who wish to understand the design in greater depth.
注：此类评论提供了有关本文件背后的基本原理的其他非必要信息。构建一致性实现不需要这些信息，但可以帮助那些希望更深入地理解设计的人。
The media feature expression syntax [1] and feature tags [2] were designed with a view to providing content media information that augments basic MIME content type information. There are some situations where it is useful to be able include that content type information in a media feature expression:
媒体功能表达式语法[1]和功能标记[2]旨在提供内容媒体信息，以增强基本MIME内容类型信息。在某些情况下，能够在媒体功能表达式中包含该内容类型信息非常有用：
o Media feature details may depend upon the content type being used. The media feature combining algebra and syntax [1] cannot apply to content type information unless it appears in the feature expression.
o 媒体功能详细信息可能取决于所使用的内容类型。结合代数和语法[1]的媒体功能无法应用于内容类型信息，除非它出现在功能表达式中。
For example, in HTTP 1.1 [4] with Transparent Content Negotiation (TCN) [5] acceptable content types and other media features are indicated in different request headers, with no clear way to indicate that they may be acceptable only in certain combinations.
例如，在具有透明内容协商（TCN）[5]的HTTP 1.1[4]中，可接受的内容类型和其他媒体功能在不同的请求头中表示，没有明确的方式表明它们可能仅在某些组合中是可接受的。
o It is sometimes useful for all media capability information to be included in a single expression. For example, DSN and MDN extensions [6] that allow a recipient to indicate media capabilities provide a single field for conveying this information.
o 有时，将所有媒体功能信息包含在单个表达式中非常有用。例如，允许收件人指示媒体功能的DSN和MDN扩展[6]提供了一个用于传递此信息的字段。
o When media features are used to describe a message content, they may refer to inner parts of a MIME composite; e.g. the component parts of a 'multipart', files in a compressed archive, or encrypted message data.
o 当媒体功能用于描述消息内容时，它们可能指MIME组合的内部部分；e、 g.“多部分”的组成部分、压缩档案中的文件或加密的消息数据。
Feature tag name Legal values
---------------- ------------
type <string>
containing a MIME content-type value.
Feature tag name Legal values
---------------- ------------
type <string>
containing a MIME content-type value.
Reference: this document, appendix A.
参考：本文件附录A。
The 'type' feature tag indicates a MIME media content type (i.e. that appears in a 'Content-type:' header of the corresponding MIME-formatted data). It must be a string of the form "type/subtype", where 'type' and 'subtype' are defined by the MIME specification [7]. Only lower-case letters should be used.
“type”功能标签表示MIME媒体内容类型（即出现在相应MIME格式数据的“content type:”标题中）。它必须是“类型/子类型”形式的字符串，其中“类型”和“子类型”由MIME规范定义[7]。只能使用小写字母。
The content type must be given without any content-type parameter values.
给定的内容类型必须没有任何内容类型参数值。
To include information in media feature expressions that is otherwise conveyed in a MIME content-type parameter, a separate media feature tag should be registered [2] and used in the media feature expression. This is illustrated by the use of 'charset' in the example at 4.1 below -- the 'charset' tag is defined by a separate registration [10].
要在媒体功能表达式中包含以其他方式在MIME内容类型参数中传递的信息，应注册单独的媒体功能标签[2]，并在媒体功能表达式中使用。下面4.1中的示例中使用了“charset”，说明了这一点——“charset”标记由单独的注册定义[10]。
NOTE: Allowing content-type parameters to be part of a type tag value was considered, but rejected because of concerns about canonicalization, ordering, case sensitivity, etc. Only exact, case-sensitive, character matching is defined for media feature expressions [1].
注意：已考虑允许内容类型参数作为类型标记值的一部分，但由于担心规范化、排序、区分大小写等问题而拒绝。仅为媒体功能表达式定义了精确、区分大小写的字符匹配[1]。
(& (type="text/plain") (charset=US-ASCII)
(color=binary) (paper-size=A4) )
(& (type="text/plain") (charset=US-ASCII)
(color=binary) (paper-size=A4) )
(& (type="image/tiff")
(color=binary)
(image-file-structure=TIFF-S)
(dpi=200)
(dpi-xyratio=[200/100,200/200])
(paper-size=A4)
(image-coding=MH) (MRC-mode=0)
(ua-media=stationery) )
(& (type="image/tiff")
(color=binary)
(image-file-structure=TIFF-S)
(dpi=200)
(dpi-xyratio=[200/100,200/200])
(paper-size=A4)
(image-coding=MH) (MRC-mode=0)
(ua-media=stationery) )
(& (type="multipart/voice-message") (VPIM-version="3.0") (audio-codec=[G726-32,GSM-610]) (audio-file-structure=[None,WAV]) (ua-terminal=mobile-handset) (audio-channels=1) )
（&（type=“multipart/voice message”）（VPIM version=“3.0”）（音频编解码器=[G726-32，GSM-610]）（音频文件结构=[None，WAV]）（ua终端=手机）（音频通道=1））
NOTE: in this case, some media features apply to MIME parts contained within the declared 'multipart/voice- message' content type. The goal here is not so much to mirror the MIME structure as to convey useful information about the (possible) message content.
注意：在这种情况下，一些媒体功能适用于声明的“multipart/voice-message”内容类型中包含的MIME部分。这里的目标与其说是镜像MIME结构，不如说是传递有关（可能的）消息内容的有用信息。
(& (pix-x<=800) (pix-y<=600)
(| (& (type="text/html") (charset=iso-8859-1)
(color=limited) )
(& (type="text/plain") (charset=US-ASCII) )
(& (type="image/gif") (color=mapped))
(& (type="image/jpeg") (color=full) ) ) )
(& (pix-x<=800) (pix-y<=600)
(| (& (type="text/html") (charset=iso-8859-1)
(color=limited) )
(& (type="text/plain") (charset=US-ASCII) )
(& (type="image/gif") (color=mapped))
(& (type="image/jpeg") (color=full) ) ) )
This example describes an HTML viewer that can deal with a limited number of color text tags, a gif viewer that supports mapped color, and a jpeg viewer that supports color.
本例描述了一个可以处理有限数量的彩色文本标记的HTML查看器、一个支持映射颜色的gif查看器和一个支持颜色的jpeg查看器。
Appendix A of this document calls for registration of a feature tag in the "IETF tree", as defined in section 3.1.1 of "Media Feature Tag Registration Procedure" [2] (i.e. these feature tags are subject to the "IETF Consensus" policies described in RFC 2434 [9]).
本文件附录A要求在“媒体功能标签注册程序”[2]第3.1.1节中定义的“IETF树”中注册功能标签（即，这些功能标签受RFC 2434[9]中描述的“IETF共识”政策的约束）。
ASN.1 identifier 1.3.6.1.8.1.30 has been assigned by the IANA for this registered feature tag and has been placed in the body of the registration.
IANA已为此注册特征标签分配ASN.1标识符1.3.6.1.8.1.30，并已将其放置在注册正文中。
This memo is not believed to introduce any security considerations that are not already inherent in the use of media feature tags and expressions [1,2].
本备忘录不会引入任何在使用媒体功能标签和表达式时尚未考虑的安全因素[1,2]。
This proposal draws from discussions in the IETF 'conneg' working group. The voice message example is based on some ideas by Glen Parsons.
本提案来自IETF“conneg”工作组的讨论。语音消息示例基于Glen Parsons的一些想法。
The author would like to thank the following people who offered comments that led to significant improvements: Ted Hardie, Larry Masinter, Paul Hoffman, Jacob Palme, Ned Freed.
作者要感谢以下提供了显著改进意见的人：特德·哈迪、拉里·马斯特恩、保罗·霍夫曼、雅各布·帕尔姆、内德·弗里德。
[1] Klyne, G., "A Syntax for Describing Media Feature Sets", RFC 2533, March 1999.
[1] Klyne，G.“描述媒体功能集的语法”，RFC2533，1999年3月。
[2] Holtman, K., Mutz, A. and T. Hardie, "Media Feature Tag Registration Procedure", RFC 2506, March 1999.
[2] Holtman，K.，Mutz，A.和T.Hardie，“媒体功能标签注册程序”，RFC 2506，1999年3月。
[3] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.
[3] Crocker，D.和P.Overell，“语法规范的扩充BNF:ABNF”，RFC 2234，1997年11月。
[4] Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068, January 1997.
[4] 菲尔丁，R.，盖蒂斯，J.，莫卧儿，J.，弗莱斯蒂克，H.和T.伯纳斯李，“超文本传输协议——HTTP/1.1”，RFC 2068，1997年1月。
[5] Holtman, K. and A. Mutz, "Transparent Content Negotiation in HTTP", RFC 2295, March 1998.
[5] Holtman，K.和A.Mutz，“HTTP中的透明内容协商”，RFC 2295，1998年3月。
[6] Wing, D., "Indicating Supported Media Features Using Extensions to DSN and MDN", RFC 2530, March 1999.
[6] Wing，D.，“使用DSN和MDN的扩展指示支持的媒体功能”，RFC2530，1999年3月。
[7] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996.
[7] Freed，N.和N.Borenstein，“多用途互联网邮件扩展（MIME）第一部分：互联网邮件正文格式”，RFC 20451996年11月。
[8] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996.
[8] Freed，N.和N.Borenstein，“多用途互联网邮件扩展（MIME）第二部分：媒体类型”，RFC 20461996年11月。
[9] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, October 1998.
[9] Narten，T.和H.Alvestrand，“在RFCs中编写IANA注意事项部分的指南”，RFC 2434，1998年10月。
[10] Hoffman, P., "Registration of Charset and Languages Media Features Tags", Work in Progress.
[10] Hoffman，P.，“字符集和语言媒体特性标签的注册”，正在进行中。
Graham Klyne Content Technologies Ltd. 1220 Parkview, Arlington Business Park Theale Reading, RG7 4SA United Kingdom
格雷厄姆·克莱恩内容技术有限公司，地址：英国RG7 4SA阿灵顿商业园Theale Reading Parkview 1220
Phone: +44 118 930 1300
Fax: +44 118 930 1301
EMail: GK@ACM.ORG
Phone: +44 118 930 1300
Fax: +44 118 930 1301
EMail: GK@ACM.ORG
Appendix A: 'Type' feature tag registration
附录A：“类型”功能标签注册
- Media Feature tag name(s):
- 媒体功能标签名称：
Type
类型
- ASN.1 identifier associated with this feature tag:
- 与此功能标签关联的ASN.1标识符：
1.3.6.1.8.1.30
1.3.6.1.8.1.30
- Summary of the media features indicated:
- 显示的媒体功能摘要：
This feature tag indicates a MIME content type that a message agent is capable of handling, or that is contained within some message data.
此功能标记表示消息代理能够处理的MIME内容类型，或包含在某些消息数据中的MIME内容类型。
The content type consists of the MIME media type and subtype, presented using all lower case letters and with any whitespace characters removed.
内容类型由MIME媒体类型和子类型组成，使用所有小写字母表示，并删除所有空白字符。
- Values appropriate for use with this feature tag:
- 适用于此功能标记的值：
String
一串
- The feature tag is intended primarily for use in the following applications, protocols, services, or negotiation mechanisms:
- 功能标签主要用于以下应用程序、协议、服务或协商机制：
Any application that wishes to convey MIME content type information in a media feature expression.
希望在媒体功能表达式中传递MIME内容类型信息的任何应用程序。
- Examples of typical use:
- 典型使用示例：
(type="image/tiff")
（type=“image/tiff”）
(& (type="text/plain") (charset=US-ASCII) )
(& (type="text/plain") (charset=US-ASCII) )
- Related standards or documents:
- 相关标准或文件：
MIME, RFC 2045 [7]
MIME，RFC 2045[7]
MIME, RFC 2046 [8]
默剧，RFC 2046[8]
Registration of Charset and Languages Media Features Tags [10]
注册字符集和语言媒体功能标签[10]
- Considerations particular to use in individual applications, protocols, services, or negotiation mechanisms:
- 在单个应用程序、协议、服务或协商机制中使用的特殊注意事项：
(N/A)
（不适用）
- Interoperability considerations:
- 互操作性注意事项：
String feature matching is case sensitive, so consistent use of case for content type values and parameters is essential if content type value matching is to be achieved in a fashion consistent with MIME content type matching.
字符串特征匹配区分大小写，因此，如果要以与MIME内容类型匹配一致的方式实现内容类型值匹配，则必须一致地使用内容类型值和参数的大小写。
Similarly, white space must be used consistently.
同样，必须始终使用空白。
This registration specifies a canonical form to be used for content type values (lower case letters and remove all whitespace).
此注册指定用于内容类型值（小写字母和删除所有空格）的规范格式。
- Related feature tags:
- 相关功能标签：
(N/A)
（不适用）
- Intended usage:
- 预期用途：
Common
常见的
- Author/Change controller:
- 作者/变更控制员：
IETF
IETF
Full Copyright Statement
完整版权声明
Copyright (C) The Internet Society (2000). All Rights Reserved.
版权所有（C）互联网协会（2000年）。版权所有。
This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.
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Acknowledgement
确认
Funding for the RFC Editor function is currently provided by the Internet Society.
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