Network Working Group G. Klyne
Request for Comments: 2738 Content Technologies
Updates: 2533 December 1999
Category: Standards Track
Network Working Group G. Klyne
Request for Comments: 2738 Content Technologies
Updates: 2533 December 1999
Category: Standards Track
Corrections to "A Syntax for Describing Media Feature Sets"
对“描述媒体功能集的语法”的更正
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 (1999). All Rights Reserved.
版权所有（C）互联网协会（1999年）。版权所有。
Abstract
摘要
In RFC 2533, "A Syntax for Describing Media Feature Sets", an expression format is presented for describing media feature capabilities using simple media feature tags.
在RFC 2533“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 contains two corrections to that specification: one fixes an error in the formal syntax specification, and the other fixes an error in the rules for reducing feature comparison predicates.
此备忘录包含对该规范的两个更正：一个修复了正式语法规范中的错误，另一个修复了减少功能比较谓词规则中的错误。
Table of Contents
目录
1. Introduction ............................................2
1.1 Terminology and document conventions 2
1.2 Discussion of this document 2
2. Correction to feature expression syntax .................3
3. Correction to feature set matching reduction rules ......3
4. Security Considerations .................................4
5. References ..............................................4
6. Author's Address ........................................4
7. Full Copyright Statement ................................5
1. Introduction ............................................2
1.1 Terminology and document conventions 2
1.2 Discussion of this document 2
2. Correction to feature expression syntax .................3
3. Correction to feature set matching reduction rules ......3
4. Security Considerations .................................4
5. References ..............................................4
6. Author's Address ........................................4
7. Full Copyright Statement ................................5
In RFC 2533, "A Syntax for Describing Media Feature Sets" [1], an expression format is presented for describing media feature capabilities using simple media feature tags. This provides a format for message handling agents to describe the media feature content of messages that they can handle. That memo also describes an algorithm for finding the common capabilities expressed by two different feature expressions.
在RFC 2533“描述媒体功能集的语法”[1]中，提供了一种表达式格式，用于使用简单的媒体功能标记描述媒体功能。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。该备忘录还描述了一种算法，用于查找由两个不同特征表达式表示的公共功能。
This memo contains two corrections to that specification: one fixes an error in the formal syntax specification, and the other fixes an error in the feature set matching algorithm, in the rules for reducing feature comparison predicates.
此备忘录包含对该规范的两个更正：一个修复了正式语法规范中的错误，另一个修复了减少特征比较谓词规则中的特征集匹配算法中的错误。
The first of these corrections affects the normative content of RFC 2533; the second affects non-normative content.
第一项修正影响RFC 2533的规范性内容；第二种影响非规范性内容。
This specification uses syntax notation and conventions described in RFC 2234, "Augmented BNF for Syntax Specifications: ABNF" [2].
本规范使用RFC 2234“语法规范的扩充BNF:ABNF”[2]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。
Discussion of this document should take place on the content negotiation and media feature registration mailing list hosted by the Internet Mail Consortium (IMC).
本文件的讨论应在互联网邮件联盟（IMC）主办的内容协商和媒体功能注册邮件列表上进行。
Please send comments regarding this document to:
请将有关本文件的意见发送至：
ietf-medfree@imc.org
ietf-medfree@imc.org
To subscribe to this list, send a message with the body 'subscribe' to "ietf-medfree-request@imc.org".
要订阅此列表，请向“ietf medfree”发送一条正文为“订阅”的消息-request@imc.org".
To see what has gone on before you subscribed, please see the mailing list archive at:
要查看订阅前的情况，请访问邮件列表存档：
http://www.imc.org/ietf-medfree/
http://www.imc.org/ietf-medfree/
In section 4.1, RFC 2533 defines the syntax for a "set" expression as follows:
在第4.1节中，RFC 2533对“集合”表达式的语法定义如下：
set = attr "=" "[" setentry *( "," setentry ) "]"
setentry = value "/" range
set = attr "=" "[" setentry *( "," setentry ) "]"
setentry = value "/" range
The production for 'setentry' should read:
“setentry”的产品应为：
setentry = value / range
setentry = value / range
That is: the '/' character is not a character literal, but separates two alternative forms for 'setentry'. This corrected syntax allows the set expression examples given in section 4.2.5 of RFC 2533, such as:
也就是说，“/”字符不是字符文字，而是分隔了“setentry”的两种可选形式。该修正语法允许RFC 2533第4.2.5节中给出的集合表达式示例，例如：
( width=[3,4,6..17/2] )
（宽度=[3,4,6..17/2]）
In section 5.8.2, "Rules for simplifying unordered values", RFC 2533 lists the following rewriting rules for simplifying feature tag comparisons with unordered values:
在第5.8.2节“简化无序值的规则”中，RFC 2533列出了以下用于简化与无序值的特征标记比较的重写规则：
(LE f a) (LE f b) --> (LE f a), a=b
FALSE, otherwise
(LE f a) (GE f b) --> FALSE, a!=b
(LE f a) (NL f b) --> (LE f a) a!=b
FALSE, otherwise
(LE f a) (NG f b) --> (LE f a), a!=b
FALSE, otherwise
(LE f a) (LE f b) --> (LE f a), a=b
FALSE, otherwise
(LE f a) (GE f b) --> FALSE, a!=b
(LE f a) (NL f b) --> (LE f a) a!=b
FALSE, otherwise
(LE f a) (NG f b) --> (LE f a), a!=b
FALSE, otherwise
The second of these rules is incomplete, and should read:
第二条规则不完整，应为：
(LE f a) (GE f b) --> (LE f a), a=b FALSE, otherwise
（LE f a）（GE f b）-->（LE f a），a=b假，否则
NOTE: implementation experience with these rules has suggested a revised feaure set matching algorithm with a more useful set of simplification rules. Apart from the change noted above, the algorithm given in RFC 2533 has been implemented and shown to work as intended, but the results generated are not always in the most convenient form. It is planned to test and publish a revised algorithm at a future date.
注：根据这些规则的实施经验，建议使用一组更有用的简化规则，改进feaure集合匹配算法。除了上述变更外，RFC 2533中给出的算法已经实现，并显示其工作正常，但生成的结果并不总是最方便的形式。计划在未来某个日期测试并发布修订后的算法。
Security considerations are discussed in RFC 2533 [1] and related documents.
RFC 2533[1]和相关文件中讨论了安全注意事项。
[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] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.
[2] Crocker，D.和P.Overell，“语法规范的扩充BNF:ABNF”，RFC 2234，1997年11月。
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阿灵顿商业园公园1220号
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
Copyright (C) The Internet Society (1999). All Rights Reserved.
版权所有（C）互联网协会（1999年）。版权所有。
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Acknowledgement
确认
Funding for the RFC Editor function is currently provided by the Internet Society.
RFC编辑功能的资金目前由互联网协会提供。