Internet Engineering Task Force (IETF) J. Klensin
Request for Comments: 5894 August 2010
Category: Informational
ISSN: 2070-1721
Internet Engineering Task Force (IETF) J. Klensin
Request for Comments: 5894 August 2010
Category: Informational
ISSN: 2070-1721
Internationalized Domain Names for Applications (IDNA): Background, Explanation, and Rationale
应用程序国际化域名（IDNA）：背景、说明和基本原理
Abstract
摘要
Several years have passed since the original protocol for Internationalized Domain Names (IDNs) was completed and deployed. During that time, a number of issues have arisen, including the need to update the system to deal with newer versions of Unicode. Some of these issues require tuning of the existing protocols and the tables on which they depend. This document provides an overview of a revised system and provides explanatory material for its components.
自从最初的国际域名协议（IDN）完成并部署以来，已经过去了几年。在此期间，出现了许多问题，包括需要更新系统以处理较新版本的Unicode。其中一些问题需要调整现有协议及其所依赖的表。本文件概述了经修订的系统，并提供了其组成部分的说明材料。
Status of This Memo
关于下段备忘
This document is not an Internet Standards Track specification; it is published for informational purposes.
本文件不是互联网标准跟踪规范；它是为了提供信息而发布的。
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). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.
本文件是互联网工程任务组（IETF）的产品。它代表了IETF社区的共识。它已经接受了公众审查，并已被互联网工程指导小组（IESG）批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准；见RFC 5741第2节。
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/rfc5894.
有关本文件当前状态、任何勘误表以及如何提供反馈的信息，请访问http://www.rfc-editor.org/info/rfc5894.
Copyright Notice
版权公告
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.
版权所有（c）2010 IETF信托基金和确定为文件作者的人员。版权所有。
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(http://trustee.ietf.org/license-info)自本文件出版之日起生效。请仔细阅读这些文件，因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本，并提供简化BSD许可证中所述的无担保。
This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English.
本文件可能包含2008年11月10日之前发布或公开的IETF文件或IETF贡献中的材料。控制某些材料版权的人员可能未授予IETF信托允许在IETF标准流程之外修改此类材料的权利。在未从控制此类材料版权的人员处获得充分许可的情况下，不得在IETF标准流程之外修改本文件，也不得在IETF标准流程之外创建其衍生作品，除了将其格式化以RFC形式发布或将其翻译成英语以外的其他语言。
Table of Contents
目录
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Context and Overview . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1. DNS "Name" Terminology . . . . . . . . . . . . . . . . 5
1.2.2. New Terminology and Restrictions . . . . . . . . . . . 6
1.3. Objectives . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4. Applicability and Function of IDNA . . . . . . . . . . . . 7
1.5. Comprehensibility of IDNA Mechanisms and Processing . . . 8
2. Processing in IDNA2008 . . . . . . . . . . . . . . . . . . . . 9
3. Permitted Characters: An Inclusion List . . . . . . . . . . . 9
3.1. A Tiered Model of Permitted Characters and Labels . . . . 10
3.1.1. PROTOCOL-VALID . . . . . . . . . . . . . . . . . . . . 10
3.1.2. CONTEXTUAL RULE REQUIRED . . . . . . . . . . . . . . . 11
3.1.2.1. Contextual Restrictions . . . . . . . . . . . . . 11
3.1.2.2. Rules and Their Application . . . . . . . . . . . 12
3.1.3. DISALLOWED . . . . . . . . . . . . . . . . . . . . . . 12
3.1.4. UNASSIGNED . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Registration Policy . . . . . . . . . . . . . . . . . . . 14
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Context and Overview . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1. DNS "Name" Terminology . . . . . . . . . . . . . . . . 5
1.2.2. New Terminology and Restrictions . . . . . . . . . . . 6
1.3. Objectives . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4. Applicability and Function of IDNA . . . . . . . . . . . . 7
1.5. Comprehensibility of IDNA Mechanisms and Processing . . . 8
2. Processing in IDNA2008 . . . . . . . . . . . . . . . . . . . . 9
3. Permitted Characters: An Inclusion List . . . . . . . . . . . 9
3.1. A Tiered Model of Permitted Characters and Labels . . . . 10
3.1.1. PROTOCOL-VALID . . . . . . . . . . . . . . . . . . . . 10
3.1.2. CONTEXTUAL RULE REQUIRED . . . . . . . . . . . . . . . 11
3.1.2.1. Contextual Restrictions . . . . . . . . . . . . . 11
3.1.2.2. Rules and Their Application . . . . . . . . . . . 12
3.1.3. DISALLOWED . . . . . . . . . . . . . . . . . . . . . . 12
3.1.4. UNASSIGNED . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Registration Policy . . . . . . . . . . . . . . . . . . . 14
3.3. Layered Restrictions: Tables, Context, Registration, and
Applications . . . . . . . . . . . . . . . . . . . . . . . 15
4. Application-Related Issues . . . . . . . . . . . . . . . . . . 15
4.1. Display and Network Order . . . . . . . . . . . . . . . . 15
4.2. Entry and Display in Applications . . . . . . . . . . . . 16
4.3. Linguistic Expectations: Ligatures, Digraphs, and
Alternate Character Forms . . . . . . . . . . . . . . . . 19
4.4. Case Mapping and Related Issues . . . . . . . . . . . . . 20
4.5. Right-to-Left Text . . . . . . . . . . . . . . . . . . . . 21
5. IDNs and the Robustness Principle . . . . . . . . . . . . . . 22
6. Front-end and User Interface Processing for Lookup . . . . . . 22
7. Migration from IDNA2003 and Unicode Version Synchronization . 25
7.1. Design Criteria . . . . . . . . . . . . . . . . . . . . . 25
7.1.1. Summary and Discussion of IDNA Validity Criteria . . . 25
7.1.2. Labels in Registration . . . . . . . . . . . . . . . . 26
7.1.3. Labels in Lookup . . . . . . . . . . . . . . . . . . . 27
7.2. Changes in Character Interpretations . . . . . . . . . . . 28
7.2.1. Character Changes: Eszett and Final Sigma . . . . . . 28
7.2.2. Character Changes: Zero Width Joiner and Zero
Width Non-Joiner . . . . . . . . . . . . . . . . . . . 29
7.2.3. Character Changes and the Need for Transition . . . . 29
7.2.4. Transition Strategies . . . . . . . . . . . . . . . . 30
7.3. Elimination of Character Mapping . . . . . . . . . . . . . 31
7.4. The Question of Prefix Changes . . . . . . . . . . . . . . 31
7.4.1. Conditions Requiring a Prefix Change . . . . . . . . . 31
7.4.2. Conditions Not Requiring a Prefix Change . . . . . . . 32
7.4.3. Implications of Prefix Changes . . . . . . . . . . . . 32
7.5. Stringprep Changes and Compatibility . . . . . . . . . . . 33
7.6. The Symbol Question . . . . . . . . . . . . . . . . . . . 33
7.7. Migration between Unicode Versions: Unassigned Code
Points . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.8. Other Compatibility Issues . . . . . . . . . . . . . . . . 36
8. Name Server Considerations . . . . . . . . . . . . . . . . . . 37
8.1. Processing Non-ASCII Strings . . . . . . . . . . . . . . . 37
8.2. Root and Other DNS Server Considerations . . . . . . . . . 37
9. Internationalization Considerations . . . . . . . . . . . . . 38
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
10.1. IDNA Character Registry . . . . . . . . . . . . . . . . . 38
10.2. IDNA Context Registry . . . . . . . . . . . . . . . . . . 39
10.3. IANA Repository of IDN Practices of TLDs . . . . . . . . . 39
11. Security Considerations . . . . . . . . . . . . . . . . . . . 39
11.1. General Security Issues with IDNA . . . . . . . . . . . . 39
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 40
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
14.1. Normative References . . . . . . . . . . . . . . . . . . . 40
14.2. Informative References . . . . . . . . . . . . . . . . . . 41
3.3. Layered Restrictions: Tables, Context, Registration, and
Applications . . . . . . . . . . . . . . . . . . . . . . . 15
4. Application-Related Issues . . . . . . . . . . . . . . . . . . 15
4.1. Display and Network Order . . . . . . . . . . . . . . . . 15
4.2. Entry and Display in Applications . . . . . . . . . . . . 16
4.3. Linguistic Expectations: Ligatures, Digraphs, and
Alternate Character Forms . . . . . . . . . . . . . . . . 19
4.4. Case Mapping and Related Issues . . . . . . . . . . . . . 20
4.5. Right-to-Left Text . . . . . . . . . . . . . . . . . . . . 21
5. IDNs and the Robustness Principle . . . . . . . . . . . . . . 22
6. Front-end and User Interface Processing for Lookup . . . . . . 22
7. Migration from IDNA2003 and Unicode Version Synchronization . 25
7.1. Design Criteria . . . . . . . . . . . . . . . . . . . . . 25
7.1.1. Summary and Discussion of IDNA Validity Criteria . . . 25
7.1.2. Labels in Registration . . . . . . . . . . . . . . . . 26
7.1.3. Labels in Lookup . . . . . . . . . . . . . . . . . . . 27
7.2. Changes in Character Interpretations . . . . . . . . . . . 28
7.2.1. Character Changes: Eszett and Final Sigma . . . . . . 28
7.2.2. Character Changes: Zero Width Joiner and Zero
Width Non-Joiner . . . . . . . . . . . . . . . . . . . 29
7.2.3. Character Changes and the Need for Transition . . . . 29
7.2.4. Transition Strategies . . . . . . . . . . . . . . . . 30
7.3. Elimination of Character Mapping . . . . . . . . . . . . . 31
7.4. The Question of Prefix Changes . . . . . . . . . . . . . . 31
7.4.1. Conditions Requiring a Prefix Change . . . . . . . . . 31
7.4.2. Conditions Not Requiring a Prefix Change . . . . . . . 32
7.4.3. Implications of Prefix Changes . . . . . . . . . . . . 32
7.5. Stringprep Changes and Compatibility . . . . . . . . . . . 33
7.6. The Symbol Question . . . . . . . . . . . . . . . . . . . 33
7.7. Migration between Unicode Versions: Unassigned Code
Points . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.8. Other Compatibility Issues . . . . . . . . . . . . . . . . 36
8. Name Server Considerations . . . . . . . . . . . . . . . . . . 37
8.1. Processing Non-ASCII Strings . . . . . . . . . . . . . . . 37
8.2. Root and Other DNS Server Considerations . . . . . . . . . 37
9. Internationalization Considerations . . . . . . . . . . . . . 38
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
10.1. IDNA Character Registry . . . . . . . . . . . . . . . . . 38
10.2. IDNA Context Registry . . . . . . . . . . . . . . . . . . 39
10.3. IANA Repository of IDN Practices of TLDs . . . . . . . . . 39
11. Security Considerations . . . . . . . . . . . . . . . . . . . 39
11.1. General Security Issues with IDNA . . . . . . . . . . . . 39
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 40
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
14.1. Normative References . . . . . . . . . . . . . . . . . . . 40
14.2. Informative References . . . . . . . . . . . . . . . . . . 41
Internationalized Domain Names in Applications (IDNA) is a collection of standards that allow client applications to convert some mnemonic strings expressed in Unicode to an ASCII-compatible encoding form ("ACE") that is a valid DNS label containing only LDH syntax (see the Definitions document [RFC5890]). The specific form of ACE label used by IDNA is called an "A-label". A client can look up an exact A-label in the existing DNS, so A-labels do not require any extensions to DNS, upgrades of DNS servers, or updates to low-level client libraries. An A-label is recognizable from the prefix "xn--" before the characters produced by the Punycode algorithm [RFC3492]; thus, a user application can identify an A-label and convert it into Unicode (or some local coded character set) for display.
应用程序中的国际化域名（IDNA）是一组标准，允许客户端应用程序将一些以Unicode表示的助记符字符串转换为ASCII兼容编码形式（“ACE”），该编码形式是一个仅包含LDH语法的有效DNS标签（见定义文档[RFC5890]）。IDNA使用的ACE标签的具体形式称为“A标签”。客户端可以在现有DNS中查找精确的A标签，因此A标签不需要对DNS进行任何扩展、升级DNS服务器或更新低级客户端库。A标签可从Punycode算法[RFC3492]产生的字符前的前缀“xn--”识别；因此，用户应用程序可以识别a标签并将其转换为Unicode（或某些本地编码字符集）以供显示。
On the registry side, IDNA allows a registry to offer Internationalized Domain Names (IDNs) for registration as A-labels. A registry may offer any subset of valid IDNs, and may apply any restrictions or bundling (grouping of similar labels together in one registration) appropriate for the context of that registry. Registration of labels is sometimes discussed separately from lookup, and it is subject to a few specific requirements that do not apply to lookup.
在注册表方面，IDNA允许注册表提供国际化域名（IDN）以注册为a标签。注册中心可以提供有效IDN的任何子集，并且可以应用适用于该注册中心上下文的任何限制或捆绑（在一次注册中将类似标签分组在一起）。标签的注册有时与查找分开讨论，并且它受到一些不适用于查找的特定要求的约束。
DNS clients and registries are subject to some differences in requirements for handling IDNs. In particular, registries are urged to register only exact, valid A-labels, while clients might do some mapping to get from otherwise-invalid user input to a valid A-label.
DNS客户端和注册表在处理IDN的要求上存在一些差异。特别是，要求注册中心只注册准确、有效的A标签，而客户端可能会进行一些映射，以从无效的用户输入获取有效的A标签。
The first version of IDNA was published in 2003 and is referred to
here as IDNA2003 to contrast it with the current version, which is
known as IDNA2008 (after the year in which IETF work started on it).
IDNA2003 consists of four documents: the IDNA base specification
[RFC3490], Nameprep [RFC3491], Punycode [RFC3492], and Stringprep
[RFC3454]. The current set of documents, IDNA2008, is not dependent
on any of the IDNA2003 specifications other than the one for Punycode
encoding. References to "IDNA2008", "these specifications", or
"these documents" are to the entire IDNA2008 set listed in a separate
Definitions document [RFC5890]. The characters that are valid in
A-labels are identified from rules listed in the Tables document
[RFC5892], but validity can be derived from the Unicode properties of
those characters with a very few exceptions.
The first version of IDNA was published in 2003 and is referred to
here as IDNA2003 to contrast it with the current version, which is
known as IDNA2008 (after the year in which IETF work started on it).
IDNA2003 consists of four documents: the IDNA base specification
[RFC3490], Nameprep [RFC3491], Punycode [RFC3492], and Stringprep
[RFC3454]. The current set of documents, IDNA2008, is not dependent
on any of the IDNA2003 specifications other than the one for Punycode
encoding. References to "IDNA2008", "these specifications", or
"these documents" are to the entire IDNA2008 set listed in a separate
Definitions document [RFC5890]. The characters that are valid in
A-labels are identified from rules listed in the Tables document
[RFC5892], but validity can be derived from the Unicode properties of
those characters with a very few exceptions.
Traditionally, DNS labels are matched case-insensitively (as described in the DNS specifications [RFC1034][RFC1035]). That convention was preserved in IDNA2003 by a case-folding operation that
传统上，DNS标签不区分大小写进行匹配（如DNS规范[RFC1034][RFC1035]中所述）。该公约在2003年IDNA2003年的一次案件折叠行动中得以保留
generally maps capital letters into lowercase ones. However, if case rules are enforced from one language, another language sometimes loses the ability to treat two characters separately. Case-insensitivity is treated slightly differently in IDNA2008.
通常将大写字母映射为小写字母。但是，如果从一种语言强制执行大小写规则，另一种语言有时会失去分别处理两个字符的能力。IDNA2008对病例不敏感的处理略有不同。
IDNA2003 used Unicode version 3.2 only. In order to keep up with new characters added in new versions of Unicode, IDNA2008 decouples its rules from any particular version of Unicode. Instead, the attributes of new characters in Unicode, supplemented by a small number of exception cases, determine how and whether the characters can be used in IDNA labels.
IDNA2003仅使用Unicode版本3.2。为了跟上新版本Unicode中添加的新字符，IDNA2008将其规则与任何特定版本的Unicode解耦。相反，Unicode中新字符的属性以及少量例外情况决定了如何以及是否可以在IDNA标签中使用这些字符。
This document provides informational context for IDNA2008, including terminology, background, and policy discussions. It contains no normative material; specifications for conformance to the IDNA2008 protocols appears entirely in the other documents in the series.
本文档提供IDNA2008的信息背景，包括术语、背景和政策讨论。它不包含任何规范性材料；IDNA2008协议的一致性规范完全出现在本系列的其他文档中。
Terminology for IDNA2008 appears in the Definitions document [RFC5890]. That document also contains a road map to the IDNA2008 document collection. No attempt should be made to understand this document without the definitions and concepts that appear there.
IDNA2008的术语见定义文档[RFC5890]。该文件还载有IDNA2008文件集的路线图。如果没有出现的定义和概念，不得试图理解本文件。
In the context of IDNs, the DNS term "name" has introduced some confusion as people speak of DNS labels in terms of the words or phrases of various natural languages. Historically, many of the "names" in the DNS have been mnemonics to identify some particular concept, object, or organization. They are typically rooted in some language because most people think in language-based ways. But, because they are mnemonics, they need not obey the orthographic conventions of any language: it is not a requirement that it be possible for them to be "words".
在IDN的上下文中，DNS术语“名称”引入了一些混淆，因为人们用各种自然语言的单词或短语来谈论DNS标签。历史上，DNS中的许多“名称”都是用于识别特定概念、对象或组织的助记符。它们通常植根于某种语言，因为大多数人以基于语言的方式思考。但是，因为它们是记忆法，所以它们不需要遵守任何语言的正字法惯例：它们不一定是“单词”。
This distinction is important because the reasonable goal of an IDN effort is not to be able to write the great Klingon (or language of one's choice) novel in DNS labels but to be able to form a usefully broad range of mnemonics in ways that are as natural as possible in a very broad range of scripts.
这种区别很重要，因为IDN工作的合理目标不是能够在DNS标签中写出伟大的克林贡语（或自己选择的语言）小说，而是能够在非常广泛的脚本中以尽可能自然的方式形成有用的广泛的助记符。
IDNA2008 introduces new terminology. Precise definitions are provided in the Definitions document for the terms U-label, A-Label, LDH label (to which all valid pre-IDNA hostnames conformed), Reserved LDH label (R-LDH label), XN-label, Fake A-label, and Non-Reserved LDH label (NR-LDH label).
IDNA2008引入了新的术语。定义文件中提供了术语U-label、A-label、LDH label（所有有效的pre-IDNA主机名均符合该术语）、保留LDH label（R-LDH label）、XN label、伪A-label和非保留LDH label（NR-LDH label）的精确定义。
In addition, the term "putative label" has been adopted to refer to a label that may appear to meet certain definitional constraints but has not yet been sufficiently tested for validity.
此外，“推定标签”一词被用来指似乎符合某些定义限制但尚未经过充分有效性检验的标签。
These definitions are also illustrated in Figure 1 of the Definitions document. R-LDH labels contain "--" in the third and fourth character positions from the beginning of the label. In IDNA-aware applications, only a subset of these reserved labels is permitted to be used, namely the A-label subset. A-labels are a subset of the R-LDH labels that begin with the case-insensitive string "xn--". Labels that bear this prefix but that are not otherwise valid fall into the "Fake A-label" category. The Non-Reserved labels (NR-LDH labels) are implicitly valid since they do not bear any resemblance to the labels specified by IDNA.
这些定义也在定义文档的图1中进行了说明。R-LDH标签在标签开头的第三和第四个字符位置包含“-”。在支持IDNA的应用程序中，仅允许使用这些保留标签的子集，即a标签子集。A标签是以不区分大小写的字符串“xn--”开头的R-LDH标签的子集。带有此前缀但在其他方面无效的标签属于“假A标签”类别。非保留标签（NR-LDH标签）隐式有效，因为它们与IDNA指定的标签没有任何相似之处。
The creation of the Reserved-LDH category is required for three reasons:
需要创建保留LDH类别有三个原因：
o to prevent confusion with pre-IDNA coding forms;
o 防止与IDNA前编码形式混淆；
o to permit future extensions that would require changing the prefix, no matter how unlikely those might be (see Section 7.4); and
o 允许将来需要更改前缀的扩展，无论这种情况多么不可能（见第7.4节）；和
o to reduce the opportunities for attacks via the Punycode encoding algorithm itself.
o 通过Punycode编码算法本身减少攻击机会。
As with other documents in the IDNA2008 set, this document uses the term "registry" to describe any zone in the DNS. That term, and the terms "zone" or "zone administration", are interchangeable.
与IDNA2008集合中的其他文档一样，本文档使用术语“注册表”来描述DNS中的任何区域。该术语与术语“区域”或“区域管理”可以互换。
These are the main objectives in revising IDNA.
这些是修订IDNA的主要目标。
o Use a more recent version of Unicode and allow IDNA to be independent of Unicode versions, so that IDNA2008 need not be updated for implementations to adopt code points from new Unicode versions.
o 使用最新版本的Unicode，并允许IDNA独立于Unicode版本，这样就不需要更新IDNA2008来实现采用新Unicode版本的代码点。
o Fix a very small number of code point categorizations that have turned out to cause problems in the communities that use those code points.
o 修复极少量的代码点分类，这些分类结果导致使用这些代码点的社区出现问题。
o Reduce the dependency on mapping, in favor of valid A-labels. This will result in pre-mapped forms that are not valid IDNA labels appearing less often in various contexts.
o 减少对映射的依赖，有利于有效的A标签。这将导致在各种上下文中出现的预映射表单不是有效的IDNA标签。
o Fix some details in the bidirectional code point handling algorithms.
o 修复双向代码点处理算法中的一些细节。
The IDNA specification solves the problem of extending the repertoire of characters that can be used in domain names to include a large subset of the Unicode repertoire.
IDNA规范解决了扩展可在域名中使用的字符集以包含大量Unicode字符集的问题。
IDNA does not extend DNS. Instead, the applications (and, by implication, the users) continue to see an exact-match lookup service. Either there is a single name that matches exactly (subject to the base DNS requirement of case-insensitive ASCII matching) or there is no match. This model has served the existing applications well, but it requires, with or without internationalized domain names, that users know the exact spelling of the domain names that are to be typed into applications such as web browsers and mail user agents. The introduction of the larger repertoire of characters potentially makes the set of misspellings larger, especially given that in some cases the same appearance, for example on a business card, might visually match several Unicode code points or several sequences of code points.
IDNA不扩展DNS。相反，应用程序（以及隐含的用户）继续看到精确的匹配查找服务。要么有一个名称完全匹配（取决于基本DNS要求的不区分大小写的ASCII匹配），要么没有匹配。该模型很好地服务于现有的应用程序，但无论是否使用国际化域名，它都要求用户知道要输入到web浏览器和邮件用户代理等应用程序中的域名的确切拼写。更大的字符库的引入可能会使拼写错误的集合更大，特别是在某些情况下，相同的外观（例如名片上）可能会在视觉上匹配多个Unicode代码点或多个代码点序列。
The IDNA standard does not require any applications to conform to it, nor does it retroactively change those applications. An application can elect to use IDNA in order to support IDNs while maintaining interoperability with existing infrastructure. For applications that want to use non-ASCII characters in public DNS domain names, IDNA is the only option that is defined at the time this specification is published. Adding IDNA support to an existing application entails changes to the application only, and leaves room for flexibility in front-end processing and more specifically in the user interface (see Section 6).
IDNA标准不要求任何应用程序符合该标准，也不追溯更改这些应用程序。应用程序可以选择使用IDNA以支持IDN，同时保持与现有基础架构的互操作性。对于希望在公共DNS域名中使用非ASCII字符的应用程序，IDNA是发布此规范时定义的唯一选项。向现有应用程序添加IDNA支持只需要对应用程序进行更改，并在前端处理和更具体地在用户界面中留出灵活性的空间（请参见第6节）。
A great deal of the discussion of IDN solutions has focused on transition issues and how IDNs will work in a world where not all of the components have been updated. Proposals that were not chosen by the original IDN Working Group would have depended on updating user applications, DNS resolvers, and DNS servers in order for a user to apply an internationalized domain name in any form or coding
关于IDN解决方案的大量讨论都集中在过渡问题上，以及在并非所有组件都已更新的世界中，IDN将如何工作。原始IDN工作组未选择的方案将取决于更新用户应用程序、DNS解析程序和DNS服务器，以便用户以任何形式或编码应用国际化域名
acceptable under that method. While processing must be performed prior to or after access to the DNS, IDNA requires no changes to the DNS protocol, any DNS servers, or the resolvers on users' computers.
在这种方法下是可以接受的。虽然必须在访问DNS之前或之后执行处理，但IDNA不需要更改DNS协议、任何DNS服务器或用户计算机上的解析程序。
IDNA allows the graceful introduction of IDNs not only by avoiding upgrades to existing infrastructure (such as DNS servers and mail transport agents), but also by allowing some limited use of IDNs in applications by using the ASCII-encoded representation of the labels containing non-ASCII characters. While such names are user-unfriendly to read and type, and hence not optimal for user input, they can be used as a last resort to allow rudimentary IDN usage. For example, they might be the best choice for display if it were known that relevant fonts were not available on the user's computer. In order to allow user-friendly input and output of the IDNs and acceptance of some characters as equivalent to those to be processed according to the protocol, the applications need to be modified to conform to this specification.
IDNA不仅避免了对现有基础设施（如DNS服务器和邮件传输代理）的升级，而且通过使用包含非ASCII字符的标签的ASCII编码表示形式，允许在应用程序中有限地使用IDN，从而允许优雅地引入IDN。虽然这样的名称对用户阅读和键入不友好，因此对于用户输入来说不是最佳的，但它们可以作为允许基本IDN使用的最后手段。例如，如果已知用户的计算机上没有相关字体，则它们可能是显示的最佳选择。为了允许用户友好地输入和输出IDN，并接受与根据协议处理的字符等效的某些字符，需要修改应用程序以符合本规范。
This version of IDNA uses the Unicode character repertoire for continuity with the original version of IDNA.
此版本的IDNA使用Unicode字符库与原始版本的IDNA保持连续性。
One goal of IDNA2008, which is aided by the main goal of reducing the dependency on mapping, is to improve the general understanding of how IDNA works and what characters are permitted and what happens to them. Comprehensibility and predictability to users and registrants are important design goals for this effort. End-user applications have an important role to play in increasing this comprehensibility.
IDNA2008的一个目标是提高对IDNA工作方式、允许哪些字符以及这些字符会发生什么的一般理解，这一目标得到了减少对映射依赖性这一主要目标的帮助。用户和注册者的可理解性和可预测性是这项工作的重要设计目标。最终用户应用程序在提高这种可理解性方面发挥着重要作用。
Any system that tries to handle international characters encounters some common problems. For example, a User Interface (UI) cannot display a character if no font containing that character is available. In some cases, internationalization enables effective localization while maintaining some global uniformity but losing some universality.
任何试图处理国际角色的系统都会遇到一些常见问题。例如，如果没有包含字符的字体可用，则用户界面（UI）无法显示该字符。在某些情况下，国际化实现了有效的本地化，同时保持了一些全球一致性，但失去了一些普遍性。
It is difficult to even make suggestions as to how end-user applications should cope when characters and fonts are not available. Because display functions are rarely controlled by the types of applications that would call upon IDNA, such suggestions will rarely be very effective.
当字符和字体不可用时，甚至很难就最终用户应用程序应如何应对提出建议。由于显示功能很少由调用IDNA的应用程序类型控制，因此此类建议很少有效。
Conversion between local character sets and normalized Unicode, if needed, is part of this set of user interface issues. Those conversions introduce complexity in a system that does not use Unicode as its primary (or only) internal character coding system. If a label is converted to a local character set that does not have
如果需要，本地字符集和规范化Unicode之间的转换是这组用户界面问题的一部分。这些转换在不使用Unicode作为其主要（或唯一）内部字符编码系统的系统中引入了复杂性。如果将标签转换为不具有
all the needed characters, or that uses different character-coding principles, the user interface program may have to add special logic to avoid or reduce loss of information.
所有需要的字符，或使用不同字符编码原则的字符，用户界面程序可能必须添加特殊逻辑以避免或减少信息丢失。
The major difficulty may lie in accurately identifying the incoming character set and applying the correct conversion routine. Even more difficult, the local character coding system could be based on conceptually different assumptions than those used by Unicode (e.g., choice of font encodings used for publications in some Indic scripts). Those differences may not easily yield unambiguous conversions or interpretations even if each coding system is internally consistent and adequate to represent the local language and script.
主要困难可能在于准确识别输入字符集并应用正确的转换例程。更为困难的是，本地字符编码系统可能基于与Unicode使用的假设不同的概念（例如，在某些印度语脚本中选择用于出版物的字体编码）。这些差异可能不容易产生明确的转换或解释，即使每个编码系统内部一致且足以表示本地语言和脚本。
IDNA2008 shifts responsibility for character mapping and other adjustments from the protocol (where it was located in IDNA2003) to pre-processing before invoking IDNA itself. The intent is that this change will lead to greater usage of fully-valid A-Labels or U-labels in display, transit, and storage, which should aid comprehensibility and predictability. A careful look at pre-processing raises issues about what that pre-processing should do and at what point pre-processing becomes harmful; how universally consistent pre-processing algorithms can be; and how to be compatible with labels prepared in an IDNA2003 context. Those issues are discussed in Section 6 and in the Mapping document [IDNA2008-Mapping].
IDNA2008将字符映射和其他调整的责任从协议（它位于IDNA2003中）转移到调用IDNA之前的预处理。其目的是，这一变化将导致在显示、运输和存储中更多地使用完全有效的A标签或U标签，这将有助于理解性和可预测性。仔细观察预处理会引发一些问题，即预处理应该做什么，以及在什么情况下预处理变得有害；预处理算法的普遍一致性；以及如何与IDNA2003上下文中准备的标签兼容。这些问题在第6节和映射文件[IDNA2008映射]中进行了讨论。
IDNA2008 separates Domain Name Registration and Lookup in the protocol specification (RFC 5891, Sections 4 and 5 [RFC5891]). Although most steps in the two processes are similar, the separation reflects current practice in which per-registry (DNS zone) restrictions and special processing are applied at registration time but not during lookup. Another significant benefit is that separation facilitates incremental addition of permitted character groups to avoid freezing on one particular version of Unicode.
IDNA2008在协议规范中分离域名注册和查找（RFC 5891，第4节和第5节[RFC5891]）。虽然这两个过程中的大多数步骤是相似的，但分离反映了当前的做法，即每个注册表（DNS区域）限制和特殊处理在注册时应用，而不是在查找期间应用。另一个显著的好处是，分离有助于增量添加允许的字符组，以避免在特定版本的Unicode上冻结。
The actual registration and lookup protocols for IDNA2008 are specified in the Protocol document.
IDNA2008的实际注册和查找协议在协议文档中指定。
IDNA2008 adopts the inclusion model. A code point is assumed to be invalid for IDN use unless it is included as part of a Unicode property-based rule or, in rare cases, included individually by an exception. When an implementation moves to a new version of Unicode, the rules may indicate new valid code points.
IDNA2008采用包含模型。除非代码点作为基于Unicode属性的规则的一部分包含，或者在极少数情况下，通过异常单独包含，否则假定代码点对于IDN使用无效。当实现移动到新版本的Unicode时，规则可能会指示新的有效代码点。
This section provides an overview of the model used to establish the algorithm and character lists of the Tables document [RFC5892] and describes the names and applicability of the categories used there. Note that the inclusion of a character in the PROTOCOL-VALID category group (Section 3.1.1) does not imply that it can be used indiscriminately; some characters are associated with contextual rules that must be applied as well.
本节概述了用于建立表格文件[RFC5892]的算法和字符列表的模型，并描述了其中使用的类别的名称和适用性。注意，在协议有效类别组（第3.1.1节）中包含字符并不意味着可以不加区别地使用；某些字符与必须应用的上下文规则相关联。
The information given in this section is provided to make the rules, tables, and protocol easier to understand. The normative generating rules that correspond to this informal discussion appear in the Tables document, and the rules that actually determine what labels can be registered or looked up are in the Protocol document.
本节提供的信息旨在使规则、表格和协议更易于理解。与此非正式讨论相对应的规范性生成规则出现在表格文档中，而实际确定可以注册或查找哪些标签的规则则出现在协议文档中。
Moving to an inclusion model involves a new specification for the list of characters that are permitted in IDNs. In IDNA2003, character validity is independent of context and fixed forever (or until the standard is replaced). However, globally context-independent rules have proved to be impractical because some characters, especially those that are called "Join_Controls" in Unicode, are needed to make reasonable use of some scripts but have no visible effect in others. IDNA2003 prohibited those types of characters entirely by discarding them. We now have a consensus that under some conditions, these "joiner" characters are legitimately needed to allow useful mnemonics for some languages and scripts. In general, context-dependent rules help deal with characters (generally characters that would otherwise be prohibited entirely) that are used differently or perceived differently across different scripts, and allow the standard to be applied more appropriately in cases where a string is not universally handled the same way.
移动到包含模型涉及IDN中允许的字符列表的新规范。在IDNA2003中，字符有效性与上下文无关，并且永远固定（或者直到标准被替换）。然而，事实证明，全局上下文无关规则是不切实际的，因为某些字符，特别是Unicode中称为“Join_Controls”的字符，需要合理使用某些脚本，但在其他脚本中没有明显的效果。IDNA2003完全禁止这些类型的字符，方法是丢弃它们。我们现在已经达成共识，在某些情况下，这些“joiner”字符是合法需要的，以便为某些语言和脚本提供有用的助记符。通常，上下文相关规则有助于处理在不同脚本中使用不同或感知不同的字符（通常是完全禁止的字符），并允许在字符串处理方式不一致的情况下更恰当地应用标准。
IDNA2008 divides all possible Unicode code points into four categories: PROTOCOL-VALID, CONTEXTUAL RULE REQUIRED, DISALLOWED, and UNASSIGNED.
IDNA2008将所有可能的Unicode代码点分为四类：协议有效、上下文规则必需、不允许和未分配。
Characters identified as PROTOCOL-VALID (often abbreviated PVALID) are permitted in IDNs. Their use may be restricted by rules about the context in which they appear or by other rules that apply to the entire label in which they are to be embedded. For example, any label that contains a character in this category that has a "right-to-left" property must be used in context with the Bidi rules [RFC5893]. The term PROTOCOL-VALID is used to stress the fact that the presence of a character in this category does not imply that a given registry need accept registrations containing any of the
IDN中允许标识为协议有效的字符（通常缩写为PVALID）。它们的使用可能受到有关它们出现的上下文的规则或适用于它们要嵌入的整个标签的其他规则的限制。例如，包含此类别中具有“从右到左”属性的字符的任何标签必须在Bidi规则[RFC5893]的上下文中使用。术语PROTOCOL-VALID用于强调这样一个事实，即此类字符的存在并不意味着给定注册表需要接受包含以下内容的注册：
characters in the category. Registries are still expected to apply judgment about labels they will accept and to maintain rules consistent with those judgments (see the Protocol document [RFC5891] and Section 3.3).
类别中的字符。注册机构仍需对其将接受的标签作出判断，并保持与这些判断一致的规则（见协议文件[RFC5891]和第3.3节）。
Characters that are placed in the PROTOCOL-VALID category are expected to never be removed from it or reclassified. While theoretically characters could be removed from Unicode, such removal would be inconsistent with the Unicode stability principles (see UTR 39: Unicode Security Mechanisms [Unicode52], Appendix F) and hence should never occur.
放置在PROTOCOL-VALID类别中的字符永远不会从中删除或重新分类。虽然理论上可以从Unicode中删除字符，但这种删除不符合Unicode稳定性原则（参见UTR 39:Unicode安全机制[Unicode52]，附录F），因此不应发生。
Some characters may be unsuitable for general use in IDNs but necessary for the plausible support of some scripts. The two most commonly cited examples are the ZERO WIDTH JOINER and ZERO WIDTH NON-JOINER characters (ZWJ, U+200D and ZWNJ, U+200C), but other characters may require special treatment because they would otherwise be DISALLOWED (typically because Unicode considers them punctuation or special symbols) but need to be permitted in limited contexts. Other characters are given this special treatment because they pose exceptional danger of being used to produce misleading labels or to cause unacceptable ambiguity in label matching and interpretation.
某些字符可能不适合在IDN中通用，但对于某些脚本的合理支持是必需的。最常引用的两个示例是零宽度连接符和零宽度非连接符字符（ZWJ，U+200D和ZWNJ，U+200C），但其他字符可能需要特殊处理，因为它们在其他情况下是不允许的（通常是因为Unicode认为它们是标点符号或特殊符号），但在有限的上下文中需要允许。其他字符被给予这种特殊处理，因为它们极有可能被用来制作误导性标签或在标签匹配和解释中造成不可接受的歧义。
Characters with contextual restrictions are identified as CONTEXTUAL RULE REQUIRED and are associated with a rule. The rule defines whether the character is valid in a particular string, and also whether the rule itself is to be applied on lookup as well as registration.
具有上下文限制的字符被标识为所需的上下文规则，并与规则关联。该规则定义字符在特定字符串中是否有效，以及规则本身是否应用于查找和注册。
A distinction is made between characters that indicate or prohibit joining and ones similar to them (known as CONTEXT-JOINER or CONTEXTJ) and other characters requiring contextual treatment (CONTEXT-OTHER or CONTEXTO). Only the former require full testing at lookup time.
在表示或禁止连接的字符和与其类似的字符（称为CONTEXT-JOINER或CONTEXTJ）以及需要上下文处理的其他字符（CONTEXT-other或CONTEXTO）之间进行了区分。只有前者需要在查找时进行全面测试。
It is important to note that these contextual rules cannot prevent all uses of the relevant characters that might be confusing or problematic. What they are expected to do is to confine applicability of the characters to scripts (and narrower contexts) where zone administrators are knowledgeable enough about the use of those characters to be prepared to deal with them appropriately.
重要的是要注意，这些上下文规则不能阻止所有可能混淆或有问题的相关字符的使用。他们需要做的是将字符的适用性限制在脚本（以及更窄的上下文）中，在脚本中，区域管理员对这些字符的使用有足够的了解，以便准备好适当地处理它们。
For example, a registry dealing with an Indic script that requires ZWJ and/or ZWNJ as part of the writing system is expected to understand where the characters have visible effect and where they do not and to make registration rules accordingly. By contrast, a registry dealing primarily with Latin or Cyrillic script might not be actively aware that the characters exist, much less about the consequences of embedding them in labels drawn from those scripts and therefore should avoid accepting registrations containing those characters, at least in labels using characters from the Latin or Cyrillic scripts.
例如，处理需要ZWJ和/或ZWNJ作为书写系统一部分的INDI脚本的注册表应了解字符在何处具有可见效果，在何处不具有可见效果，并相应地制定注册规则。相比之下，主要处理拉丁或西里尔文字的注册中心可能不会主动意识到这些字符的存在，更不用说将它们嵌入从这些文字中提取的标签的后果了，因此应该避免接受包含这些字符的注册，至少在标签中使用来自拉丁或西里尔文字的字符。
Rules have descriptions such as "Must follow a character from Script XYZ", "Must occur only if the entire label is in Script ABC", or "Must occur only if the previous and subsequent characters have the DFG property". The actual rules may be DEFINED or NULL. If present, they may have values of "True" (character may be used in any position in any label), "False" (character may not be used in any label), or may be a set of procedural rules that specify the context in which the character is permitted.
规则具有诸如“必须跟随脚本XYZ中的字符”、“仅当整个标签在脚本ABC中时必须出现”或“仅当前面和后面的字符具有DFG属性时必须出现”等描述。实际规则可能已定义或为空。如果存在，它们的值可能为“真”（字符可以在任何标签的任何位置使用）、“假”（字符不能在任何标签中使用），或者可能是一组程序规则，用于指定允许字符的上下文。
Because it is easier to identify these characters than to know that they are actually needed in IDNs or how to establish exactly the right rules for each one, a rule may have a null value in a given version of the tables. Characters associated with null rules are not permitted to appear in putative labels for either registration or lookup. Of course, a later version of the tables might contain a non-null rule.
由于识别这些字符比知道IDN中实际需要它们或如何为每个字符建立正确的规则更容易，因此规则在给定版本的表中可能有空值。与空规则关联的字符不允许出现在注册或查找的假定标签中。当然，表的更高版本可能包含非空规则。
The actual rules and their descriptions are in Sections 2 and 3 of the Tables document [RFC5892]. That document also specifies the creation of a registry for future rules.
实际规则及其说明见表格文件[RFC5892]的第2节和第3节。该文件还规定为今后的规则建立登记册。
Some characters are inappropriate for use in IDNs and are thus excluded for both registration and lookup (i.e., IDNA-conforming applications performing name lookup should verify that these characters are absent; if they are present, the label strings should be rejected rather than converted to A-labels and looked up. Some of these characters are problematic for use in IDNs (such as the FRACTION SLASH character, U+2044), while some of them (such as the various HEART symbols, e.g., U+2665, U+2661, and U+2765, see Section 7.6) simply fall outside the conventions for typical identifiers (basically letters and numbers).
有些字符不适合在IDN中使用，因此在注册和查找时都被排除在外（即，执行名称查找的符合IDNA的应用程序应验证这些字符是否存在；如果存在，则应拒绝标签字符串，而不是将其转换为A标签并进行查找。其中一些字符在IDN中使用时存在问题（例如分数斜杠字符，U+2044），而其中一些字符（例如各种心脏符号，例如U+2665、U+2661和U+2765，见第7.6节）只是不属于典型标识符（基本上是字母和数字）的约定范围。
Of course, this category would include code points that had been removed entirely from Unicode should such removals ever occur.
当然，这一类别将包括在发生此类删除时完全从Unicode中删除的代码点。
Characters that are placed in the DISALLOWED category are expected to never be removed from it or reclassified. If a character is classified as DISALLOWED in error and the error is sufficiently problematic, the only recourse would be either to introduce a new code point into Unicode and classify it as PROTOCOL-VALID or for the IETF to accept the considerable costs of an incompatible change and replace the relevant RFC with one containing appropriate exceptions.
放置在不允许类别中的字符永远不会从中删除或重新分类。如果某个字符被归类为错误不允许，并且该错误存在足够多的问题，唯一的办法是在Unicode中引入一个新的代码点，并将其归类为协议有效的代码点，或者让IETF接受不兼容更改的巨大成本，并用包含适当例外的RFC替换相关RFC。
There is provision for exception cases but, in general, characters are placed into DISALLOWED if they fall into one or more of the following groups:
有例外情况的规定，但一般来说，如果字符属于以下一个或多个组，则将其置于“不允许”状态：
o The character is a compatibility equivalent for another character. In slightly more precise Unicode terms, application of Normalization Form KC (NFKC) to the character yields some other character.
o 该字符是另一个字符的兼容等效项。在更精确的Unicode术语中，对字符应用规范化形式KC（NFKC）会产生其他字符。
o The character is an uppercase form or some other form that is mapped to another character by Unicode case folding.
o 字符是大写形式或通过Unicode大小写折叠映射到另一个字符的其他形式。
o The character is a symbol or punctuation form or, more generally, something that is not a letter, digit, or a mark that is used to form a letter or digit.
o 字符是一种符号或标点符号形式，或者更一般地说，它不是字母、数字或用于形成字母或数字的标记。
For convenience in processing and table-building, code points that do not have assigned values in a given version of Unicode are treated as belonging to a special UNASSIGNED category. Such code points are prohibited in labels to be registered or looked up. The category differs from DISALLOWED in that code points are moved out of it by the simple expedient of being assigned in a later version of Unicode (at which point, they are classified into one of the other categories as appropriate).
为了便于处理和表构建，在给定版本的Unicode中没有赋值的代码点被视为属于特殊的未赋值类别。禁止在要注册或查找的标签中使用此类代码点。该类别与不允许的不同之处在于，通过在更高版本的Unicode中分配代码点（此时，它们被适当地划分为其他类别之一），代码点被移出该类别。
The rationale for restricting the processing of UNASSIGNED characters is simply that the properties of such code points cannot be completely known until actual characters are assigned to them. For example, assume that an UNASSIGNED code point were included in a label to be looked up. Assume that the code point was later assigned to a character that required some set of contextual rules. With that combination, un-updated instances of IDNA-aware software might permit lookup of labels containing the previously unassigned characters while updated versions of the software might restrict use of the same
限制未分配字符处理的理由很简单，就是在实际字符分配给这些代码点之前，无法完全了解这些代码点的属性。例如，假设要查找的标签中包含未分配的代码点。假设代码点后来被分配给需要一组上下文规则的字符。通过这种组合，IDNA感知软件的未更新实例可能允许查找包含以前未分配字符的标签，而软件的更新版本可能会限制相同字符的使用
label in lookup, depending on the contextual rules. It should be clear that under no circumstance should an UNASSIGNED character be permitted in a label to be registered as part of a domain name.
查找中的标签，具体取决于上下文规则。应该清楚的是，在任何情况下都不允许在标签中使用未分配字符作为域名的一部分进行注册。
While these recommendations cannot and should not define registry policies, registries should develop and apply additional restrictions as needed to reduce confusion and other problems. For example, it is generally believed that labels containing characters from more than one script are a bad practice although there may be some important exceptions to that principle. Some registries may choose to restrict registrations to characters drawn from a very small number of scripts. For many scripts, the use of variant techniques such as those as described in the JET specification for the CJK script [RFC3743] and its generalization [RFC4290], and illustrated for Chinese by the tables provided by the Chinese Domain Name Consortium [RFC4713] may be helpful in reducing problems that might be perceived by users.
虽然这些建议不能也不应该界定登记册政策，但登记册应根据需要制定和实施额外的限制，以减少混乱和其他问题。例如，一般认为，包含多个脚本字符的标签是一种不好的做法，尽管这一原则可能有一些重要的例外。一些注册中心可能会选择将注册限制为从极少量脚本中提取的字符。对于许多脚本，使用各种技术，如CJK脚本[RFC3743]及其泛化[RFC4290]的JET规范中所述的技术，以及中国域名联盟[RFC4713]提供的中文表格中所示的技术，可能有助于减少用户可能察觉到的问题。
In general, users will benefit if registries only permit characters from scripts that are well-understood by the registry or its advisers. If a registry decides to reduce opportunities for confusion by constructing policies that disallow characters used in historic writing systems or characters whose use is restricted to specialized, highly technical contexts, some relevant information may be found in Section 2.4 (Specific Character Adjustments) of Unicode Identifier and Pattern Syntax [Unicode-UAX31], especially Table 4 (Candidate Characters for Exclusion from Identifiers), and Section 3.1 (General Security Profile for Identifiers) in Unicode Security Mechanisms [Unicode-UTS39].
一般来说，如果注册中心只允许来自注册中心或其顾问很好理解的脚本的字符，那么用户将受益。如果注册中心决定通过制定政策，禁止在历史书写系统中使用字符或仅在专业化、高度技术性的上下文中使用字符，以减少混淆的机会，则可在第2.4节（特定字符调整）中找到一些相关信息Unicode安全机制[Unicode-UTS39]中的Unicode标识符和模式语法[Unicode-UAX31]，特别是表4（从标识符中排除的候选字符）和第3.1节（标识符的通用安全配置文件）。
The requirement (in Section 4.1 of the Protocol document [RFC5891]) that registration procedures use only U-labels and/or A-labels is intended to ensure that registrants are fully aware of exactly what is being registered as well as encouraging use of those canonical forms. That provision should not be interpreted as requiring that registrants need to provide characters in a particular code sequence. Registrant input conventions and management are part of registrant-registrar interactions and relationships between registries and registrars and are outside the scope of these standards.
协议文件[RFC5891]第4.1节要求注册程序仅使用U型标签和/或A型标签，旨在确保注册人完全了解正在注册的内容，并鼓励使用这些规范形式。该规定不应解释为要求注册人需要提供特定代码序列中的字符。注册人输入约定和管理是注册人与注册人之间的互动和关系的一部分，不属于这些标准的范围。
It is worth stressing that these principles of policy development and application apply at all levels of the DNS, not only, e.g., top level domain (TLD) or second level domain (SLD) registrations. Even a trivial, "anything is permitted that is valid under the protocol" policy is helpful in that it helps users and application developers know what to expect.
值得强调的是，这些政策制定和应用原则不仅适用于顶级域（TLD）或二级域（SLD）注册等DNS的所有级别。即使是一个微不足道的“协议下任何有效的内容都是允许的”策略也很有帮助，因为它可以帮助用户和应用程序开发人员知道期望得到什么。
3.3. Layered Restrictions: Tables, Context, Registration, and Applications
3.3. 分层限制：表、上下文、注册和应用程序
The character rules in IDNA2008 are based on the realization that there is no single magic bullet for any of the security, confusability, or other issues associated with IDNs. Instead, the specifications define a variety of approaches. The character tables are the first mechanism, protocol rules about how those characters are applied or restricted in context are the second, and those two in combination constitute the limits of what can be done in the protocol. As discussed in the previous section (Section 3.2), registries are expected to restrict what they permit to be registered, devising and using rules that are designed to optimize the balance between confusion and risk on the one hand and maximum expressiveness in mnemonics on the other.
IDNA2008中的字符规则基于这样一种认识，即对于任何与IDN相关的安全性、易混淆性或其他问题，都没有单一的魔弹。相反，规范定义了多种方法。字符表是第一种机制，关于如何在上下文中应用或限制这些字符的协议规则是第二种机制，而这两种规则的组合构成了协议中可以执行的操作的限制。如前一节（第3.2节）所述，注册处应限制其允许注册的内容，设计并使用旨在优化混淆和风险与最大助记功能表达能力之间平衡的规则。
In addition, there is an important role for user interface programs in warning against label forms that appear problematic given their knowledge of local contexts and conventions. Of course, no approach based on naming or identifiers alone can protect against all threats.
此外，鉴于用户界面程序对本地上下文和约定的了解，用户界面程序在警告出现问题的标签表单方面发挥着重要作用。当然，仅仅基于命名或标识符的方法无法抵御所有威胁。
Domain names are always transmitted in network order (the order in which the code points are sent in protocols), but they may have a different display order (the order in which the code points are displayed on a screen or paper). When a domain name contains characters that are normally written right to left, display order may be affected although network order is not. It gets even more complicated if left-to-right and right-to-left labels are adjacent to each other within a domain name. The decision about the display order is ultimately under the control of user agents -- including Web browsers, mail clients, hosted Web applications and many more -- which may be highly localized. Should a domain name abc.def, in which both labels are represented in scripts that are written right to left, be displayed as fed.cba or cba.fed? Applications that are in deployment today are already diverse, and one can find examples of either choice.
域名总是以网络顺序（以协议形式发送代码点的顺序）传输，但它们可能具有不同的显示顺序（代码点在屏幕或纸张上的显示顺序）。当域名包含通常从右向左写入的字符时，显示顺序可能会受到影响，尽管网络顺序不受影响。如果从左到右和从右到左的标签在一个域名内彼此相邻，情况就变得更加复杂了。关于显示顺序的决定最终由用户代理控制——包括Web浏览器、邮件客户端、托管Web应用程序等——这些代理可能是高度本地化的。如果域名abc.def中的两个标签都以从右向左写入的脚本表示，那么该域名是否应显示为fed.cba或cba.fed？今天部署的应用程序已经多种多样，您可以找到任何一种选择的示例。
The picture changes once again when an IDN appears in an Internationalized Resource Identifier (IRI) [RFC3987]. An IRI or internationalized email address contains elements other than the domain name. For example, IRIs contain protocol identifiers and field delimiter syntax such as "http://" or "mailto:" while email addresses contain the "@" to separate local parts from domain names.
当IDN出现在国际化资源标识符（IRI）[RFC3987]中时，情况再次发生变化。IRI或国际化电子邮件地址包含域名以外的元素。例如，IRI包含协议标识符和字段分隔符语法，如“http://”或“mailto:”，而电子邮件地址包含“@”以将本地部分与域名分开。
An IRI in network order begins with "http://" followed by domain labels in network order, thus "http://abc.def".
网络顺序的IRI以“http://”开头，然后是网络顺序的域标签，因此http://abc.def".
User interface programs are not required to display and allow input of IRIs directly but often do so. Implementers have to choose whether the overall direction of these strings will always be left to right (or right to left) for an IRI or email address. The natural order for a user typing a domain name on a right-to-left system is fed.cba. Should the right-to-left (RTL) user interface reverse the entire domain name each time a domain name is typed? Does this change if the user types "http://" right before typing a domain name, thus implying that the user is beginning at the beginning of the network-order IRI? Experience in the 1980s and 1990s with mixing systems in which domain name labels were read in network order (left to right) and those in which those labels were read right to left would predict a great deal of confusion.
用户界面程序不需要直接显示和允许输入虹膜，但通常这样做。对于IRI或电子邮件地址，实现者必须选择这些字符串的总体方向是否总是从左到右（或从右到左）。用户在从右向左的系统上键入域名的自然顺序是fed.cba。每次键入域名时，从右向左（RTL）用户界面是否应该反转整个域名？如果用户在键入域名之前键入“http://”，这是否会改变，从而意味着用户是从网络订单IRI的开头开始的？20世纪80年代和90年代的经验表明，按照网络顺序（从左到右）读取域名标签和从右到左读取这些标签的混合系统会带来很大的混乱。
If each implementation of each application makes its own decisions on these issues, users will develop heuristics that will sometimes fail when switching applications. However, while some display order conventions, voluntarily adopted, would be desirable to reduce confusion, such suggestions are beyond the scope of these specifications.
如果每个应用程序的每个实现都对这些问题做出自己的决定，那么用户将开发出一些启发式方法，在切换应用程序时，这些方法有时会失败。然而，尽管自愿采用的一些显示顺序约定有助于减少混淆，但此类建议超出了这些规范的范围。
Applications can accept and display domain names using any character set or character coding system. The IDNA protocol does not necessarily affect the interface between users and applications. An IDNA-aware application can accept and display internationalized domain names in two formats: as the internationalized character set(s) supported by the application (i.e., an appropriate local representation of a U-label) and as an A-label. Applications may allow the display of A-labels, but are encouraged not to do so except as an interface for special purposes, possibly for debugging, or to cope with display limitations. In general, they should allow, but not encourage, user input of A-labels. A-labels are opaque and ugly, and malicious variations on them are not easily detected by users. Where possible, they should thus only be exposed when they are absolutely needed. Because IDN labels can be rendered either as A-labels or U-labels, the application may reasonably have an option for the user to select the preferred method of display. Rendering the U-label should normally be the default.
应用程序可以使用任何字符集或字符编码系统接受和显示域名。IDNA协议不一定会影响用户和应用程序之间的接口。支持IDNA的应用程序可以接受和显示两种格式的国际化域名：作为应用程序支持的国际化字符集（即U标签的适当本地表示形式）和a标签。应用程序可能允许显示A标签，但建议不要这样做，除非是作为特殊用途的接口，可能是为了调试或处理显示限制。一般来说，他们应该允许但不鼓励用户输入A标签。A标签不透明且难看，用户不容易检测到标签上的恶意变体。因此，在可能的情况下，应仅在绝对需要时才将其暴露。由于IDN标签可以呈现为A标签或U标签，因此应用程序可以合理地为用户选择首选的显示方法。渲染U标签通常应为默认设置。
Domain names are often stored and transported in many places. For example, they are part of documents such as mail messages and web pages. They are transported in many parts of many protocols, such as both the control commands of SMTP and associated message body parts,
域名经常在许多地方存储和传输。例如，它们是文档（如邮件和网页）的一部分。它们在许多协议的许多部分中传输，例如SMTP的控制命令和相关的邮件正文部分，
and in the headers and the body content in HTTP. It is important to remember that domain names appear both in domain name slots and in the content that is passed over protocols, and it would be helpful if protocols explicitly define what their domain name slots are.
在HTTP中的头和正文内容中。重要的是要记住，域名同时出现在域名槽和通过协议传递的内容中，如果协议明确定义了它们的域名槽，这将非常有用。
In protocols and document formats that define how to handle specification or negotiation of charsets, labels can be encoded in any charset allowed by the protocol or document format. If a protocol or document format only allows one charset, the labels must be given in that charset. Of course, not all charsets can properly represent all labels. If a U-label cannot be displayed in its entirety, the only choice (without loss of information) may be to display the A-label.
在定义如何处理字符集规范或协商的协议和文档格式中，标签可以用协议或文档格式允许的任何字符集编码。如果协议或文档格式只允许一个字符集，则必须在该字符集中给出标签。当然，并非所有字符集都能正确地表示所有标签。如果U型标签不能全部显示，唯一的选择（不丢失信息）可能是显示a型标签。
Where a protocol or document format allows IDNs, labels should be in whatever character encoding and escape mechanism the protocol or document format uses in the local environment. This provision is intended to prevent situations in which, e.g., UTF-8 domain names appear embedded in text that is otherwise in some other character coding.
如果协议或文档格式允许IDN，则标签应采用协议或文档格式在本地环境中使用的任何字符编码和转义机制。本规定旨在防止出现UTF-8域名嵌入其他字符编码文本中的情况。
All protocols that use domain name slots (see Section 2.3.2.6 in the Definitions document [RFC5890]) already have the capacity for handling domain names in the ASCII charset. Thus, A-labels can inherently be handled by those protocols.
所有使用域名插槽的协议（参见定义文档[RFC5890]中的第2.3.2.6节）都已具备处理ASCII字符集中域名的能力。因此，A标签本质上可以由这些协议处理。
IDNA2008 does not specify required mappings between one character or code point and others. An extended discussion of mapping issues appears in Section 6 and specific recommendations appear in the Mapping document [IDNA2008-Mapping]. In general, IDNA2008 prohibits characters that would be mapped to others by normalization or other rules. As examples, while mathematical characters based on Latin ones are accepted as input to IDNA2003, they are prohibited in IDNA2008. Similarly, uppercase characters, double-width characters, and other variations are prohibited as IDNA input although mapping them as needed in user interfaces is strongly encouraged.
IDNA2008未指定一个字符或代码点与其他字符或代码点之间所需的映射。映射问题的详细讨论见第6节，具体建议见映射文件[IDNA2008映射]。通常，IDNA2008禁止通过规范化或其他规则映射到其他字符。例如，虽然基于拉丁字母的数学字符被接受为IDNA2003的输入，但在IDNA2008中它们是被禁止的。同样，禁止将大写字符、双宽度字符和其他变体作为IDNA输入，尽管强烈鼓励在用户界面中根据需要映射它们。
Since the rules in the Tables document [RFC5892] have the effect that only strings that are not transformed by NFKC are valid, if an application chooses to perform NFKC normalization before lookup, that operation is safe since this will never make the application unable to look up any valid string. However, as discussed above, the application cannot guarantee that any other application will perform that mapping, so it should be used only with caution and for informed users.
由于表格文档[RFC5892]中的规则的作用是，只有未经NFKC转换的字符串才有效，因此，如果应用程序选择在查找之前执行NFKC规范化，则该操作是安全的，因为这永远不会使应用程序无法查找任何有效字符串。但是，如上所述，该应用程序无法保证任何其他应用程序都将执行该映射，因此只能谨慎使用，并供知情用户使用。
In many cases, these prohibitions should have no effect on what the user can type as input to the lookup process. It is perfectly reasonable for systems that support user interfaces to perform some character mapping that is appropriate to the local environment. This would normally be done prior to actual invocation of IDNA. At least conceptually, the mapping would be part of the Unicode conversions discussed above and in the Protocol document [RFC5891]. However, those changes will be local ones only -- local to environments in which users will clearly understand that the character forms are equivalent. For use in interchanges among systems, it appears to be much more important that U-labels and A-labels can be mapped back and forth without loss of information.
在许多情况下，这些禁止应该不会影响用户可以输入什么作为查找过程的输入。支持用户界面的系统执行一些适合本地环境的字符映射是完全合理的。这通常在实际调用IDNA之前完成。至少在概念上，映射是上面和协议文档[RFC5891]中讨论的Unicode转换的一部分。但是，这些更改将仅限于本地更改—对于用户将清楚地了解字符形式是等效的环境，这些更改是本地更改。对于用于系统间的交换，更重要的是可以在不丢失信息的情况下来回映射U标签和A标签。
One specific, and very important, instance of this strategy arises with case folding. In the ASCII-only DNS, names are looked up and matched in a case-independent way, but no actual case folding occurs. Names can be placed in the DNS in either uppercase or lowercase form (or any mixture of them) and that form is preserved, returned in queries, and so on. IDNA2003 approximated that behavior for non-ASCII strings by performing case folding at registration time (resulting in only lowercase IDNs in the DNS) and when names were looked up.
这种策略的一个具体且非常重要的例子就是案例折叠。在仅ASCII的DNS中，名称以独立于大小写的方式查找和匹配，但不会发生实际的大小写折叠。名称可以以大写或小写形式（或任意混合形式）放置在DNS中，并且该形式将被保留，并在查询中返回，等等。IDNA2003通过在注册时（在DNS中只产生小写IDN）和查找名称时执行大小写折叠来近似非ASCII字符串的行为。
As suggested earlier in this section, it appears to be desirable to do as little character mapping as possible as long as Unicode works correctly (e.g., Normalization Form C (NFC) mapping to resolve different codings for the same character is still necessary although the specifications require that it be performed prior to invoking the protocol) in order to make the mapping between A-labels and U-labels idempotent. Case mapping is not an exception to this principle. If only lowercase characters can be registered in the DNS (i.e., be present in a U-label), then IDNA2008 should prohibit uppercase characters as input even though user interfaces to applications should probably map those characters. Some other considerations reinforce this conclusion. For example, in ASCII case mapping for individual characters, uppercase(character) is always equal to uppercase(lowercase(character)). That may not be true with IDNs. In some scripts that use case distinctions, there are a few characters that do not have counterparts in one case or the other. The relationship between uppercase and lowercase may even be language-dependent, with different languages (or even the same language in different areas) expecting different mappings. User interface programs can meet the expectations of users who are accustomed to the case-insensitive DNS environment by performing case folding prior to IDNA processing, but the IDNA procedures themselves should neither require such mapping nor expect them when they are not natural to the localized environment.
正如本节前面所建议的，只要Unicode工作正常，就应该尽可能少地进行字符映射（例如，尽管规范要求在调用协议之前执行规范化形式C（NFC）映射，以解析同一字符的不同编码，但仍然有必要）为了使A标签和U标签之间的映射是幂等的。案例映射也不例外。如果DNS中只能注册小写字符（即U型标签中存在），则IDNA2008应禁止输入大写字符，即使应用程序的用户界面可能应映射这些字符。其他一些考虑因素强化了这一结论。例如，在单个字符的ASCII大小写映射中，大写（字符）始终等于大写（小写（字符））。IDN可能不是这样。在一些使用区分大小写的脚本中，有一些字符在一种或另一种情况下没有对应的字符。大写字母和小写字母之间的关系甚至可能依赖于语言，不同的语言（甚至不同区域的同一语言）需要不同的映射。通过在IDNA处理之前执行大小写折叠，用户界面程序可以满足习惯于不区分大小写DNS环境的用户的期望，但IDNA过程本身既不需要这样的映射，也不应该在本地化环境中不自然的情况下期望这样的映射。
4.3. Linguistic Expectations: Ligatures, Digraphs, and Alternate Character Forms
4.3. 语言期望：连字、有向图和交替字符形式
Users have expectations about character matching or equivalence that are based on their own languages and the orthography of those languages. These expectations may not always be met in a global system, especially if multiple languages are written using the same script but using different conventions. Some examples:
用户对基于他们自己的语言和这些语言的正字法的字符匹配或对等有期望。在一个全局系统中，这些期望可能并不总是得到满足，尤其是如果使用相同脚本但使用不同约定编写多种语言时。一些例子：
o A Norwegian user might expect a label with the ae-ligature to be treated as the same label as one using the Swedish spelling with a-diaeresis even though applying that mapping to English would be astonishing to users.
o 一个挪威用户可能期望一个带有ae连字的标签与一个使用瑞典语拼写和A-diaeresis的标签被视为相同的标签，即使将这种映射应用到英语会让用户感到惊讶。
o A German user might expect a label with an o-umlaut and a label that had "oe" substituted, but was otherwise the same, to be treated as equivalent even though that substitution would be a clear error in Swedish.
o 德国用户可能会期望使用o-umlaut的标签和替换了“oe”但在其他方面相同的标签被视为等效标签，即使替换在瑞典语中是一个明显的错误。
o A Chinese user might expect automatic matching of Simplified and Traditional Chinese characters, but applying that matching for Korean or Japanese text would create considerable confusion.
o 中国用户可能希望自动匹配简体和繁体汉字，但将这种匹配应用于韩文或日文文本会造成相当大的混乱。
o An English user might expect "theater" and "theatre" to match.
o 英国用户可能希望“剧院”和“剧院”匹配。
A number of languages use alphabetic scripts in which single phonemes are written using two characters, termed a "digraph", for example, the "ph" in "pharmacy" and "telephone". (Such characters can also appear consecutively without forming a digraph, as in "tophat".) Certain digraphs may be indicated typographically by setting the two characters closer together than they would be if used consecutively to represent different phonemes. Some digraphs are fully joined as ligatures. For example, the word "encyclopaedia" is sometimes set with a U+00E6 LATIN SMALL LIGATURE AE. When ligature and digraph forms have the same interpretation across all languages that use a given script, application of Unicode normalization generally resolves the differences and causes them to match. When they have different interpretations, matching must utilize other methods, presumably chosen at the registry level, or users must be educated to understand that matching will not occur.
许多语言使用字母脚本，其中单个音素使用两个字符书写，称为“有向图”，例如，“药房”和“电话”中的“ph”。（这些字符也可以连续出现，而不形成有向图，如“tophat”中）。某些有向图可以通过将两个字符设置得比连续使用以表示不同音素时更靠近来以排版方式表示。一些有向图作为连字完全连接。例如，“百科全书”一词有时带有U+00E6拉丁小连字AE。当连字和有向图形式在使用给定脚本的所有语言中具有相同的解释时，Unicode规范化的应用通常会解决差异并使它们匹配。当它们有不同的解释时，匹配必须使用其他方法，可能是在注册表级别选择的，或者必须教育用户理解匹配不会发生。
The nature of the problem can be illustrated by many words in the Norwegian language, where the "ae" ligature is the 27th letter of a 29-letter extended Latin alphabet. It is equivalent to the 28th letter of the Swedish alphabet (also containing 29 letters), U+00E4 LATIN SMALL LETTER A WITH DIAERESIS, for which an "ae" cannot be substituted according to current orthographic standards. That character (U+00E4) is also part of the German alphabet where, unlike
这个问题的本质可以用挪威语中的许多单词来说明，其中“ae”连字是一个29个字母的扩展拉丁字母表中的第27个字母。它相当于瑞典字母表的第28个字母（也包含29个字母），U+00E4拉丁文小写字母A，带有分音符，根据当前的拼写标准，“ae”不能替代。该字符（U+00E4）也是德语字母表的一部分，与
in the Nordic languages, the two-character sequence "ae" is usually treated as a fully acceptable alternate orthography for the "umlauted a" character. The inverse is however not true, and those two characters cannot necessarily be combined into an "umlauted a". This also applies to another German character, the "umlauted o" (U+00F6 LATIN SMALL LETTER O WITH DIAERESIS) which, for example, cannot be used for writing the name of the author "Goethe". It is also a letter in the Swedish alphabet where, like the "a with diaeresis", it cannot be correctly represented as "oe" and in the Norwegian alphabet, where it is represented, not as "o with diaeresis", but as "slashed o", U+00F8.
在北欧语言中，两个字符序列“ae”通常被视为“umlauted a”字符完全可接受的替代正字法。然而，相反的情况并非如此，这两个字符不一定能组合成一个“umlauted a”。这也适用于另一个德语字符“umlauted o”（U+00F6拉丁文小写字母o，带分音符），例如，它不能用于书写作者的名字“歌德”。它也是瑞典字母表中的一个字母，与“带分音符的a”一样，不能正确表示为“oe”，而在挪威字母表中，它表示为“带分音符的o”，而不是“带分音符的o”，U+00F8。
Some of the ligatures that have explicit code points in Unicode were given special handling in IDNA2003 and now pose additional problems in transition. See Section 7.2.
一些在Unicode中具有显式代码点的连字在IDNA2003中得到了特殊处理，现在在转换过程中带来了额外的问题。见第7.2节。
Additional cases with alphabets written right to left are described in Section 4.5.
第4.5节描述了字母从右向左书写的其他情况。
Matching and comparison algorithm selection often requires information about the language being used, context, or both -- information that is not available to IDNA or the DNS. Consequently, IDNA2008 makes no attempt to treat combined characters in any special way. A registry that is aware of the language context in which labels are to be registered, and where that language sometimes (or always) treats the two-character sequences as equivalent to the combined form, should give serious consideration to applying a "variant" model [RFC3743][RFC4290] or to prohibiting registration of one of the forms entirely, to reduce the opportunities for user confusion and fraud that would result from the related strings being registered to different parties.
匹配和比较算法选择通常需要有关所用语言、上下文或两者的信息——IDNA或DNS无法获得的信息。因此，IDNA2008没有试图以任何特殊方式处理组合字符。如果登记处了解标签登记的语言环境，并且该语言有时（或始终）将两个字符序列视为等同于组合形式，则应认真考虑采用“变体”模式[RFC3743][RFC4290]，或完全禁止其中一种形式的登记，减少因向不同方注册相关字符串而导致用户混淆和欺诈的机会。
In the DNS, ASCII letters are stored with their case preserved. Matching during the query process is case-independent, but none of the information that might be represented by choices of case has been lost. That model has been accidentally helpful because, as people have created DNS labels by catenating words (or parts of words) to form labels, case has often been used to distinguish among components and make the labels more memorable.
在DNS中，ASCII字母存储时保留大小写。查询过程中的匹配是独立于大小写的，但可能由大小写选项表示的信息没有丢失。该模型意外地起到了帮助作用，因为人们通过链接单词（或单词的一部分）来创建DNS标签，所以大小写通常用于区分组件，并使标签更容易记住。
Since DNS servers do not get involved in parsing IDNs, they cannot do case-independent matching. Thus, keeping the cases separate in lookup or registration, and doing matching at the server, is not feasible with IDNA or any similar approach. Matching of characters that are considered to differ only by case must be done, if desired, by programs invoking IDNA lookup even though it wasn't done by ASCII-
由于DNS服务器不参与解析IDN，因此它们无法进行独立于大小写的匹配。因此，在查找或注册中保持案例分离，并在服务器上进行匹配，对于IDNA或任何类似的方法都是不可行的。如果需要，必须通过调用IDNA查找的程序（即使不是由ASCII完成）来完成仅按大小写不同的字符的匹配-
only DNS clients. That situation was recognized in IDNA2003 and nothing in IDNA2008 fundamentally changes it or could do so. In IDNA2003, all characters are case folded and mapped by clients in a standardized step.
只有DNS客户端。这种情况在IDNA2003中得到了承认，IDNA2008中没有任何内容能够从根本上改变这种情况。在IDNA2003中，所有字符都是按标准步骤由客户端进行大小写折叠和映射的。
Even in scripts that generally support case distinctions, some characters do not have uppercase forms. For example, the Unicode case-folding operation maps Greek Final Form Sigma (U+03C2) to the medial form (U+03C3) and maps Eszett (German Sharp S, U+00DF) to "ss". Neither of these mappings is reversible because the uppercase of U+03C3 is the uppercase Sigma (U+03A3) and "ss" is an ASCII string. IDNA2008 permits, at the risk of some incompatibility, slightly more flexibility in this area by avoiding case folding and treating these characters as themselves. Approaches to handling one-way mappings are discussed in Section 7.2.
即使在通常支持区分大小写的脚本中，有些字符也没有大写形式。例如，Unicode大小写折叠操作将希腊的最终形式Sigma（U+03C2）映射到中间形式（U+03C3），并将Eszett（德语夏普S，U+00DF）映射到“ss”。这两种映射都不可逆，因为U+03C3的大写字母是大写的Sigma（U+03A3），而“ss”是ASCII字符串。IDNA2008允许，冒着某些不兼容的风险，通过避免大小写折叠并将这些字符视为自己的字符，在这方面稍微有一些灵活性。第7.2节讨论了处理单向映射的方法。
Because IDNA2003 maps Final Sigma and Eszett to other characters, and the reverse mapping is never possible, neither Final Sigma nor Eszett can be represented in the ACE form of IDNA2003 IDN nor in the native character (U-label) form derived from it. With IDNA2008, both characters can be used in an IDN and so the A-label used for lookup for any U-label containing those characters is now different. See Section 7.1 for a discussion of what kinds of changes might require the IDNA prefix to change; after extended discussions, the IDNABIS Working Group came to consensus that the change for these characters did not justify a prefix change.
由于IDNA2003将最终Sigma和Eszett映射到其他字符，并且反向映射是不可能的，因此最终Sigma和Eszett既不能以IDNA2003 IDN的ACE形式表示，也不能以其派生的本机字符（U标签）形式表示。使用IDNA2008，这两个字符都可以在IDN中使用，因此用于查找包含这些字符的任何U标签的A标签现在不同了。请参阅第7.1节，了解哪些类型的更改可能需要更改IDNA前缀；经过长时间的讨论，IDNABIS工作组达成共识，即这些字符的更改并不能证明前缀更改是合理的。
In order to be sure that the directionality of right-to-left text is unambiguous, IDNA2003 required that any label in which right-to-left characters appear both starts and ends with them and that it does not include any characters with strong left-to-right properties (that excludes other alphabetic characters but permits European digits). Any other string that contains a right-to-left character and does not meet those requirements is rejected. This is one of the few places where the IDNA algorithms (both in IDNA2003 and in IDNA2008) examine an entire label, not just individual characters. The algorithmic model used in IDNA2003 rejects the label when the final character in a right-to-left string requires a combining mark in order to be correctly represented.
为了确保从右到左文本的方向性是明确的，IDNA2003要求出现从右到左字符的任何标签都以它们开头和结尾，并且不包括任何具有强从左到右属性的字符（不包括其他字母字符，但允许欧洲数字）。任何其他包含从右向左字符且不满足这些要求的字符串都将被拒绝。这是IDNA算法（在IDNA2003和IDNA2008中）检查整个标签而不仅仅是单个字符的少数几个地方之一。当右向左字符串中的最后一个字符需要组合标记才能正确表示时，IDNA2003中使用的算法模型拒绝标签。
That prohibition is not acceptable for writing systems for languages written with consonantal alphabets to which diacritical vocalic systems are applied, and for languages with orthographies derived from them where the combining marks may have different functionality. In both cases, the combining marks can be essential components of the orthography. Examples of this are Yiddish, written with an extended
这种禁止对于使用辅音字母书写的语言的书写系统来说是不可接受的，因为辅音字母使用了变音发音系统，而对于使用从辅音字母派生的正字法的语言来说，组合标记可能具有不同的功能。在这两种情况下，组合标记可以是正字法的基本组成部分。这方面的例子有意第绪语，用扩展的
Hebrew script, and Dhivehi (the official language of Maldives), which is written in the Thaana script (which is, in turn, derived from the Arabic script). IDNA2008 removes the restriction on final combining characters with a new set of rules for right-to-left scripts and their characters. Those new rules are specified in the Bidi document [RFC5893].
希伯莱文字和Dhivehi（马尔代夫的官方语言），用Thana文字书写（而Thana文字又源于阿拉伯语）。IDNA2008为从右到左的脚本及其字符提供了一套新的规则，从而取消了对最终组合字符的限制。投标文件[RFC5893]中规定了这些新规则。
The "Robustness Principle" is often stated as "Be conservative about what you send and liberal in what you accept" (see, e.g., Section 1.2.2 of the applications-layer Host Requirements specification [RFC1123]). This principle applies to IDNA. In applying the principle to registries as the source ("sender") of all registered and useful IDNs, registries are responsible for being conservative about what they register and put out in the Internet. For IDNs to work well, zone administrators (registries) must have and require sensible policies about what is registered -- conservative policies -- and implement and enforce them.
“稳健性原则”通常被称为“对发送的内容保持保守，对接受的内容保持自由”（例如，参见应用层主机需求规范[RFC1123]第1.2.2节）。这一原则适用于IDNA。在将这一原则适用于作为所有已注册和有用的IDN来源（“发送者”）的登记处时，登记处有责任保守其在互联网上注册和发布的内容。要使IDN正常工作，区域管理员（注册中心）必须拥有并需要有关注册内容的合理策略（保守策略），并实施和强制执行这些策略。
Conversely, lookup applications are expected to reject labels that clearly violate global (protocol) rules (no one has ever seriously claimed that being liberal in what is accepted requires being stupid). However, once one gets past such global rules and deals with anything sensitive to script or locale, it is necessary to assume that garbage has not been placed into the DNS, i.e., one must be liberal about what one is willing to look up in the DNS rather than guessing about whether it should have been permitted to be registered.
相反，人们期望查找应用程序拒绝明显违反全局（协议）规则的标签（从来没有人认真声称，在被接受的内容上自由要求愚蠢）。然而，一旦人们通过了这些全局规则并处理了任何对脚本或语言环境敏感的事情，就有必要假设垃圾没有被放入DNS，也就是说，人们必须对自己愿意在DNS中查找的内容持开放态度，而不是猜测它是否应该被允许注册。
If a string cannot be successfully found in the DNS after the lookup processing described here, it makes no difference whether it simply wasn't registered or was prohibited by some rule at the registry. Application implementers should be aware that where DNS wildcards are used, the ability to successfully resolve a name does not guarantee that it was actually registered.
如果在此处描述的查找处理之后，无法在DNS中成功找到字符串，那么它是否只是未注册或被注册表中的某些规则禁止也没有区别。应用程序实现者应该知道，在使用DNS通配符的情况下，成功解析名称的能力并不保证名称已实际注册。
Domain names may be identified and processed in many contexts. They may be typed in by users themselves or embedded in an identifier such as an email address, URI, or IRI. They may occur in running text or be processed by one system after being provided in another. Systems may try to normalize URLs to determine (or guess) whether a reference is valid or if two references point to the same object without actually looking the objects up (comparison without lookup is necessary for URI types that are not intended to be resolved). Some of these goals may be more easily and reliably satisfied than others.
域名可以在许多上下文中识别和处理。它们可以由用户自己输入，也可以嵌入到诸如电子邮件地址、URI或IRI之类的标识符中。它们可能出现在正在运行的文本中，或者在另一个系统中提供后由一个系统处理。系统可能会尝试规范化URL，以确定（或猜测）引用是否有效，或者两个引用是否指向同一对象而没有实际查找对象（对于不打算解析的URI类型，需要进行无查找的比较）。其中一些目标可能比其他目标更容易、更可靠地实现。
While there are strong arguments for any domain name that is placed "on the wire" -- transmitted between systems -- to be in the zero-ambiguity forms of A-labels, it is inevitable that programs that process domain names will encounter U-labels or variant forms.
尽管有强有力的论据支持任何“在线”的域名（在系统之间传输）采用A标签的零歧义形式，但处理域名的程序不可避免地会遇到U标签或变体形式。
An application that implements the IDNA protocol [RFC5891] will always take any user input and convert it to a set of Unicode code points. That user input may be acquired by any of several different input methods, all with differing conversion processes to be taken into consideration (e.g., typed on a keyboard, written by hand onto some sort of digitizer, spoken into a microphone and interpreted by a speech-to-text engine, etc.). The process of taking any particular user input and mapping it into a Unicode code point may be a simple one: if a user strikes the "A" key on a US English keyboard, without any modifiers such as the "Shift" key held down, in order to draw a Latin small letter A ("a"), many (perhaps most) modern operating system input methods will produce to the calling application the code point U+0061, encoded in a single octet.
实现IDNA协议[RFC5891]的应用程序将始终接受任何用户输入并将其转换为一组Unicode代码点。该用户输入可以通过几种不同的输入方法中的任何一种来获取，所有这些方法都需要考虑不同的转换过程（例如，在键盘上键入、手动写入某种数字化仪、对着麦克风讲话以及由语音到文本引擎解释等）。获取任何特定用户输入并将其映射到Unicode代码点的过程可能很简单：如果用户在美式英语键盘上敲击“a”键，而不使用任何修饰语，例如按住“Shift”键，以便绘制拉丁小写字母a（“a”），则可能会有很多（可能是大多数）现代操作系统输入方法将向调用应用程序生成代码点U+0061，编码为一个八位字节。
Sometimes the process is somewhat more complicated: a user might strike a particular set of keys to represent a combining macron followed by striking the "A" key in order to draw a Latin small letter A with a macron above it. Depending on the operating system, the input method chosen by the user, and even the parameters with which the application communicates with the input method, the result might be the code point U+0101 (encoded as two octets in UTF-8 or UTF-16, four octets in UTF-32, etc.), the code point U+0061 followed by the code point U+0304 (again, encoded in three or more octets, depending upon the encoding used) or even the code point U+FF41 followed by the code point U+0304 (and encoded in some form). These examples leave aside the issue of operating systems and input methods that do not use Unicode code points for their character set.
有时，这个过程有些复杂：用户可能敲击一组特定的键来表示一个组合宏，然后敲击“a”键，以便在上面画一个带宏的拉丁文小写字母a。根据操作系统、用户选择的输入法，甚至应用程序与输入法通信的参数，结果可能是代码点U+0101（在UTF-8或UTF-16中编码为两个八位字节，在UTF-32中编码为四个八位字节，等等），代码点U+0061后接代码点U+0304（同样，根据使用的编码方式，编码为三个或更多个八位字节）或甚至代码点U+FF41后接代码点U+0304（并以某种形式编码）。这些示例忽略了操作系统和输入方法不使用Unicode代码点作为其字符集的问题。
In every case, applications (with the help of the operating systems on which they run and the input methods used) need to perform a mapping from user input into Unicode code points.
在任何情况下，应用程序（在运行它们的操作系统和使用的输入方法的帮助下）都需要执行从用户输入到Unicode代码点的映射。
IDNA2003 used a model whereby input was taken from the user, mapped (via whatever input method mechanisms were used) to a set of Unicode code points, and then further mapped to a set of Unicode code points using the Nameprep profile [RFC3491]. In this procedure, there are two separate mapping steps: first, a mapping done by the input method (which might be controlled by the operating system, the application, or some combination) and then a second mapping performed by the Nameprep portion of the IDNA protocol. The mapping done in Nameprep includes a particular mapping table to re-map some characters to other characters, a particular normalization, and a set of prohibited characters.
IDNA2003使用了一种模型，即从用户获取输入，映射（通过使用的任何输入方法机制）到一组Unicode代码点，然后使用Nameprep配置文件[RFC3491]进一步映射到一组Unicode代码点。在这个过程中，有两个单独的映射步骤：首先，由输入方法完成映射（可能由操作系统、应用程序或某些组合控制），然后由IDNA协议的Nameprep部分执行第二个映射。在Nameprep中完成的映射包括一个用于将某些字符重新映射到其他字符的特定映射表、一个特定的规范化以及一组禁止的字符。
Note that the result of the two-step mapping process means that the mapping chosen by the operating system or application in the first step might differ significantly from the mapping supplied by the Nameprep profile in the second step. This has advantages and disadvantages. Of course, the second mapping regularizes what gets looked up in the DNS, making for better interoperability between implementations that use the Nameprep mapping. However, the application or operating system may choose mappings in their input methods, which when passed through the second (Nameprep) mapping result in characters that are "surprising" to the end user.
请注意，两步映射过程的结果意味着第一步中操作系统或应用程序选择的映射可能与第二步中Nameprep概要文件提供的映射有很大不同。这有优点也有缺点。当然，第二个映射规范了在DNS中查找的内容，使得使用Nameprep映射的实现之间的互操作性更好。但是，应用程序或操作系统可能会在其输入方法中选择映射，当通过第二个（Nameprep）映射时，会产生最终用户“惊讶”的字符。
The other important feature of IDNA2003 is that, with very few exceptions, it assumes that any set of Unicode code points provided to the Nameprep mapping can be mapped into a string of Unicode code points that are "sensible", even if that means mapping some code points to nothing (that is, removing the code points from the string). This allowed maximum flexibility in input strings.
IDNA2003的另一个重要特性是，除了极少数例外，它假设提供给Nameprep映射的任何一组Unicode代码点都可以映射到一个“合理”的Unicode代码点字符串，即使这意味着将一些代码点映射为零（即从字符串中删除代码点）。这使得输入字符串具有最大的灵活性。
The present version of IDNA (IDNA2008) differs significantly in approach from the original version. First and foremost, it does not provide explicit mapping instructions. Instead, it assumes that the application (perhaps via an operating system input method) will do whatever mapping it requires to convert input into Unicode code points. This has the advantage of giving flexibility to the application to choose a mapping that is suitable for its user given specific user requirements, and avoids the two-step mapping of the original protocol. Instead of a mapping, IDNA2008 provides a set of categories that can be used to specify the valid code points allowed in a domain name.
IDNA的当前版本（IDNA2008）在方法上与原始版本存在显著差异。首先也是最重要的是，它没有提供明确的映射说明。相反，它假定应用程序（可能通过操作系统输入法）将执行将输入转换为Unicode代码点所需的任何映射。这样做的优点是，应用程序可以灵活地选择适合其特定用户需求的映射，并且避免了原始协议的两步映射。IDNA2008提供的不是映射，而是一组类别，可用于指定域名中允许的有效代码点。
In principle, an application ought to take user input of a domain name and convert it to the set of Unicode code points that represent the domain name the user intends. As a practical matter, of course, determining user intent is a tricky business, so an application needs to choose a reasonable mapping from user input. That may differ based on the particular circumstances of a user, depending on locale, language, type of input method, etc. It is up to the application to make a reasonable choice.
原则上，应用程序应该接受用户输入的域名，并将其转换为代表用户想要的域名的一组Unicode代码点。当然，实际上，确定用户意图是一项棘手的工作，因此应用程序需要从用户输入中选择合理的映射。这可能因用户的特定情况而有所不同，具体取决于区域设置、语言、输入方法的类型等。由应用程序做出合理的选择。
As mentioned above and in the IAB review and recommendations for IDNs [RFC4690], two key goals of the IDNA2008 design are:
如上所述，在IAB对IDN的审查和建议[RFC4690]中，IDNA2008设计的两个关键目标是：
o to enable applications to be agnostic about whether they are being run in environments supporting any Unicode version from 3.2 onward.
o 使应用程序不知道它们是否在支持3.2以后的任何Unicode版本的环境中运行。
o to permit incrementally adding new characters, character groups, scripts, and other character collections as they are incorporated into Unicode, doing so without disruption and, in the long term, without "heavy" processes (an IETF consensus process is required by the IDNA2008 specifications and is expected to be required and used until significant experience accumulates with IDNA operations and new versions of Unicode).
o 允许在将新字符、字符组、脚本和其他字符集合合并到Unicode中时以增量方式添加新字符、字符组、脚本和其他字符集合，这样做不会中断，从长远来看，也不会出现“繁重”的过程（IDNA2008规范要求IETF协商一致过程，预计在IDNA操作和Unicode新版本积累大量经验之前，IETF协商一致过程将被要求和使用）。
The general criteria for a label to be considered valid under IDNA are (the actual rules are rigorously defined in the Protocol [RFC5891] and Tables [RFC5892] documents):
根据IDNA，标签被视为有效的一般标准是（实际规则在协议[RFC5891]和表[RFC5892]文档中严格定义）：
o The characters are "letters", marks needed to form letters, numerals, or other code points used to write words in some language. Symbols, drawing characters, and various notational characters are intended to be permanently excluded. There is no evidence that they are important enough to Internet operations or internationalization to justify expansion of domain names beyond the general principle of "letters, digits, and hyphen". (Additional discussion and rationale for the symbol decision appears in Section 7.6.)
o 这些字符是“字母”，是构成字母、数字或其他用于在某种语言中书写单词的代码点所需的标记。符号、图形字符和各种符号字符将被永久排除在外。没有证据表明它们对互联网运营或国际化的重要性足以证明域名的扩展超出了“字母、数字和连字符”的一般原则。（第7.6节对符号决定的其他讨论和理由进行了说明。）
o Other than in very exceptional cases, e.g., where they are needed to write substantially any word of a given language, punctuation characters are excluded. The fact that a word exists is not proof that it should be usable in a DNS label, and DNS labels are not expected to be usable for multiple-word phrases (although they are certainly not prohibited if the conventions and orthography of a particular language cause that to be possible).
o 除了在非常特殊的情况下，例如，需要他们书写给定语言的任何单词，标点符号除外。一个单词存在的事实并不能证明它应该在DNS标签中可用，并且DNS标签也不能用于多个单词短语（尽管如果特定语言的约定和正字法导致这一点成为可能，那么DNS标签肯定不会被禁止）。
o Characters that are unassigned (have no character assignment at all) in the version of Unicode being used by the registry or application are not permitted, even on lookup. The issues involved in this decision are discussed in Section 7.7.
o 注册表或应用程序使用的Unicode版本中不允许未分配（根本没有字符分配）的字符，即使在查找时也是如此。第7.7节讨论了本决定涉及的问题。
o Any character that is mapped to another character by a current version of NFKC is prohibited as input to IDNA (for either registration or lookup). With a few exceptions, this principle excludes any character mapped to another by Nameprep [RFC3491].
o 当前版本的NFKC映射到另一个字符的任何字符都禁止作为IDNA的输入（用于注册或查找）。除少数例外情况外，此原则不包括通过Nameprep[RFC3491]映射到另一个字符的任何字符。
The principles above drive the design of rules that are specified exactly in the Tables document. Those rules identify the characters that are valid under IDNA. The rules themselves are normative, and the tables are derived from them, rather than vice versa.
上述原则推动了规则的设计，这些规则在表格文档中明确指定。这些规则标识IDNA下有效的字符。规则本身是规范性的，表格是从规则中派生出来的，而不是从规则中派生出来的。
Any label registered in a DNS zone must be validated -- i.e., the criteria for that label must be met -- in order for applications to work as intended. This principle is not new. For example, since the DNS was first deployed, zone administrators have been expected to verify that names meet "hostname" requirements [RFC0952] where those requirements are imposed by the expected applications. Other applications contexts, such as the later addition of special service location formats [RFC2782] imposed new requirements on zone administrators. For zones that will contain IDNs, support for Unicode version-independence requires restrictions on all strings placed in the zone. In particular, for such zones (the exact rules appear in Section 4 of the Protocol document [RFC5891]):
必须验证在DNS区域中注册的任何标签，即必须满足该标签的标准，才能使应用程序按预期工作。这一原则并不新鲜。例如，自DNS首次部署以来，区域管理员需要验证名称是否满足“主机名”要求[RFC0952]，而这些要求是由预期的应用程序强加的。其他应用环境，如后来添加的特殊服务位置格式[RFC2782]，对区域管理员提出了新的要求。对于将包含IDN的区域，对Unicode版本独立性的支持要求限制放置在该区域中的所有字符串。特别是，对于此类区域（具体规则见协议文件[RFC5891]第4节）：
o Any label that appears to be an A-label, i.e., any label that starts in "xn--", must be valid under IDNA, i.e., they must be valid A-labels, as discussed in Section 2 above.
o 任何看似A标签的标签，即任何以“xn-”开头的标签，必须在IDNA下有效，即它们必须是有效的A标签，如上文第2节所述。
o The Unicode tables (i.e., tables of code points, character classes, and properties) and IDNA tables (i.e., tables of contextual rules such as those that appear in the Tables document), must be consistent on the systems performing or validating labels to be registered. Note that this does not require that tables reflect the latest version of Unicode, only that all tables used on a given system are consistent with each other.
o Unicode表（即代码点、字符类和属性的表）和IDNA表（即上下文规则的表，如表文档中出现的那些），在执行或验证要注册的标签的系统上必须一致。请注意，这并不要求表反映最新版本的Unicode，只要求给定系统上使用的所有表彼此一致。
Under this model, registry tables will need to be updated (both the Unicode-associated tables and the tables of permitted IDN characters) to enable a new script or other set of new characters. The registry will not be affected by newer versions of Unicode, or newly authorized characters, until and unless it wishes to support them. The zone administrator is responsible for verifying validity for IDNA as well as its local policies -- a more extensive set of checks than are required for looking up the labels. Systems looking up or
在此模型下，需要更新注册表表（Unicode关联表和允许的IDN字符表），以启用新脚本或其他一组新字符。除非注册中心希望支持新版本的Unicode或新授权的字符，否则注册中心将不受其影响。区域管理员负责验证IDNA及其本地策略的有效性——这是一组比查找标签所需的更广泛的检查。正在查找或删除的系统
resolving DNS labels, especially IDN DNS labels, must be able to assume that applicable registration rules were followed for names entered into the DNS.
解析DNS标签，尤其是IDN DNS标签，必须能够假设输入DNS的名称遵循了适用的注册规则。
Any application processing a label through IDNA so it can be looked up in a DNS zone is required to (the exact rules appear in Section 5 of the Protocol document [RFC5891]):
任何通过IDNA处理标签以便在DNS区域中查找的应用程序都需要（协议文档[RFC5891]第5节中给出了确切的规则）：
o Maintain IDNA and Unicode tables that are consistent with regard to versions, i.e., unless the application actually executes the classification rules in the Tables document [RFC5892], its IDNA tables must be derived from the version of Unicode that is supported more generally on the system. As with registration, the tables need not reflect the latest version of Unicode, but they must be consistent.
o 维护版本一致的IDNA和Unicode表格，即，除非应用程序实际执行表格文档[RFC5892]中的分类规则，否则其IDNA表格必须派生自系统上更普遍支持的Unicode版本。与注册一样，表不需要反映最新版本的Unicode，但它们必须一致。
o Validate the characters in labels to be looked up only to the extent of determining that the U-label does not contain "DISALLOWED" code points or code points that are unassigned in its version of Unicode.
o 仅在确定U型标签不包含“不允许的”代码点或Unicode版本中未指定的代码点的范围内，验证要查找的标签中的字符。
o Validate the label itself for conformance with a small number of whole-label rules. In particular, it must verify that:
o 验证标签本身是否符合少量完整标签规则。特别是，它必须核实：
* there are no leading combining marks,
* 没有前导组合标记，
* the Bidi conditions are met if right-to-left characters appear,
* 如果出现从右向左的字符，则满足Bidi条件，
* any required contextual rules are available, and
* 任何必要的上下文规则都可用，并且
* any contextual rules that are associated with joiner characters (and CONTEXTJ characters more generally) are tested.
* 测试与joiner字符（以及更一般的CONTEXTJ字符）关联的任何上下文规则。
o Do not reject labels based on other contextual rules about characters, including mixed-script label prohibitions. Such rules may be used to influence presentation decisions in the user interface, but not to avoid looking up domain names.
o 不要拒绝基于其他有关字符的上下文规则的标签，包括混合脚本标签禁止。这些规则可用于影响用户界面中的表示决策，但不能避免查找域名。
To further clarify the rules about handling characters that require contextual rules, note that one can have a context-required character (i.e., one that requires a rule), but no rule. In that case, the character is treated the same way DISALLOWED characters are treated, until and unless a rule is supplied. That state is more or less equivalent to "the idea of permitting this character is accepted in principle, but it won't be permitted in practice until consensus is reached on a safe way to use it".
为了进一步阐明有关处理需要上下文规则的字符的规则，请注意，可以有上下文所需的字符（即需要规则的字符），但没有规则。在这种情况下，字符的处理方式与不允许字符的处理方式相同，除非提供了规则。这种状态或多或少相当于“允许这种性质的想法在原则上是可以接受的，但在实践中是不允许的，除非就安全使用它的方式达成共识”。
The ability to add a rule more or less exempts these characters from the prohibition against reclassifying characters from DISALLOWED to PVALID.
添加规则的能力或多或少免除了这些字符从DISALLOWED重新分类为PVALID的禁令。
And, obviously, "no rule" is different from "have a rule, but the test either succeeds or fails".
显然，“无规则”不同于“有规则，但测试要么成功，要么失败”。
Lookup applications that follow these rules, rather than having their own criteria for rejecting lookup attempts, are not sensitive to version incompatibilities with the particular zone registry associated with the domain name except for labels containing characters recently added to Unicode.
遵循这些规则的查找应用程序（而不是有自己的拒绝查找尝试的标准）对与域名关联的特定区域注册表的版本不兼容不敏感，但包含最近添加到Unicode的字符的标签除外。
An application or client that processes names according to this protocol and then resolves them in the DNS will be able to locate any name that is registered, as long as those registrations are valid under IDNA and its version of the IDNA tables is sufficiently up to date to interpret all of the characters in the label. Messages to users should distinguish between "label contains an unallocated code point" and other types of lookup failures. A failure on the basis of an old version of Unicode may lead the user to a desire to upgrade to a newer version, but will have no other ill effects (this is consistent with behavior in the transition to the DNS when some hosts could not yet handle some forms of names or record types).
根据此协议处理名称，然后在DNS中解析名称的应用程序或客户端将能够找到已注册的任何名称，只要这些注册在IDNA下有效，并且其IDNA表的版本足够最新，能够解释标签中的所有字符。发送给用户的消息应区分“标签包含未分配的代码点”和其他类型的查找失败。基于旧版本Unicode的故障可能会导致用户希望升级到新版本，但不会产生其他不良影响（这与某些主机无法处理某些形式的名称或记录类型时向DNS过渡的行为一致）。
As a consequence of the elimination of mapping, the current version of IDNA changes the interpretation of a few characters relative to its predecessors. This subsection outlines the issues and discusses possible transition strategies.
由于消除了映射，当前版本的IDNA改变了相对于其前身的一些字符的解释。本小节概述了这些问题，并讨论了可能的过渡策略。
In those scripts that make case distinctions, there are a few characters for which an obvious and unique uppercase character has not historically been available to match a lowercase one, or vice versa. For those characters, the mappings used in constructing the Stringprep tables for IDNA2003, performed using the Unicode toCaseFold operation (see Section 5.18 of the Unicode Standard [Unicode52]), generate different characters or sets of characters. Those operations are not reversible and lose even more information than traditional uppercase or lowercase transformations, but are more useful than those transformations for comparison purposes. Two notable characters of this type are the German character Eszett (Sharp S, U+00DF) and the Greek Final Form Sigma (U+03C2). The former is case folded to the ASCII string "ss", the latter to a medial (lowercase) Sigma (U+03C3).
在那些区分大小写的脚本中，有几个字符的明显且唯一的大写字符在历史上从未与小写字符匹配，反之亦然。对于这些字符，使用Unicode toCaseFold操作（参见Unicode标准[Unicode52]第5.18节）为IDNA2003构建Stringprep表时使用的映射生成不同的字符或字符集。这些操作是不可逆的，与传统的大写或小写转换相比，它们丢失的信息甚至更多，但在比较方面比那些转换更有用。这种类型的两个显著字符是德语字符Eszett（夏普S，U+00DF）和希腊语的最后形式Sigma（U+03C2）。前者大小写折叠为ASCII字符串“ss”，后者为中间（小写）Sigma（U+03C3）。
IDNA2003 mapped both ZERO WIDTH JOINER (ZWJ, U+200D) and ZERO WIDTH NON-JOINER (ZWNJ, U+200C) to nothing, effectively dropping these characters from any label in which they appeared and treating strings containing them as identical to strings that did not. As discussed in Section 3.1.2 above, those characters are essential for writing many reasonable mnemonics for certain scripts. However, treating them as valid in IDNA2008, even with contextual restrictions, raises approximately the same problem as exists with Eszett and Final Sigma: strings that were valid under IDNA2003 have different interpretations as labels, and different A-labels, than the same strings under this newer version.
IDNA2003将零宽度JOINER（ZWJ，U+200D）和零宽度NON-JOINER（ZWNJ，U+200C）映射为nothing，有效地将这些字符从它们出现的任何标签中删除，并将包含它们的字符串视为与不包含它们的字符串相同。如上文第3.1.2节所述，这些字符对于为某些脚本编写许多合理的助记符至关重要。然而，在IDNA2008中将其视为有效的，即使有上下文限制，也会引发与Eszett和最终西格玛存在的问题大致相同的问题：在IDNA2003下有效的字符串与此新版本下相同的字符串具有不同的标签解释和不同的A标签。
The decision to eliminate mandatory and standardized mappings, including case folding, from the IDNA2008 protocol in order to make A-labels and U-labels idempotent made these characters problematic. If they were to be disallowed, important words and mnemonics could not be written in orthographically reasonable ways. If they were to be permitted as distinct characters, there would be no information loss and registries would have more flexibility, but IDNA2003 and IDNA2008 lookups might result in different A-labels.
为了使A-标签和U-标签幂等元，从IDNA2008协议中消除强制性和标准化映射（包括大小写折叠）的决定使这些字符成为问题。如果它们被禁止，重要的单词和记忆法就不能以正字法合理的方式书写。如果允许它们作为不同的字符，则不会丢失信息，注册中心将具有更大的灵活性，但IDNA2003和IDNA2008查找可能会导致不同的A标签。
With the understanding that there would be incompatibility either way but a judgment that the incompatibility was not significant enough to justify a prefix change, the Working Group concluded that Eszett and Final Form Sigma should be treated as distinct and Protocol-Valid characters.
工作组了解到，无论哪种方式都会存在不兼容，但判断不兼容程度不足以证明前缀更改的合理性，因此得出结论，Eszett和最终形式的Sigma应被视为不同且协议有效的字符。
Since these characters are interpreted in different ways under the older and newer versions of IDNA, transition strategies and policies will be necessary. Some actions can reasonably be taken by applications' client programs (those that perform lookup operations or cause them to be performed), but because of the diversity of situations and uses of the DNS, much of the responsibility will need to fall on registries.
由于在IDNA的旧版本和新版本下，这些字符的解释方式不同，因此过渡策略和政策将是必要的。应用程序的客户端程序（执行查找操作或导致执行查找操作的客户端程序）可以合理地采取一些操作，但由于DNS的情况和使用的多样性，大部分责任将落在注册中心身上。
Registries, especially those maintaining zones for third parties, must decide how to introduce a new service in a way that does not create confusion or significantly weaken or invalidate existing identifiers. This is not a new problem; registries were faced with similar issues when IDNs were introduced (potentially, and especially for Latin-based scripts, in conflict with existing labels that had been rendered in ASCII characters by applying more or less standardized conventions) and when other new forms of strings have been permitted as labels.
注册中心，特别是那些为第三方维护区域的注册中心，必须决定如何以不造成混淆或显著削弱或使现有标识符无效的方式引入新服务。这不是一个新问题；当引入IDN时（特别是对于基于拉丁语的脚本，可能与通过应用或多或少的标准化约定以ASCII字符呈现的现有标签冲突），以及当允许其他新形式的字符串作为标签时，注册中心也面临类似的问题。
There are several approaches to the introduction of new characters or changes in interpretation of existing characters from their mapped forms in the earlier version of IDNA. The transition issue is complicated because the forms of these labels after the ToUnicode(ToASCII()) translation in IDNA2003 not only remain valid but do not provide strong indications of what the registrant intended: a string containing "ss" could have simply been intended to be that string or could have been intended to contain an Eszett; a string containing lowercase Sigma could have been intended to contain Final Sigma (one might make heuristic guesses based on position in a string, but the long tradition of forming labels by concatenating words makes such heuristics unreliable), and strings that do not contain ZWJ or ZWNJ might have been intended to contain them. Without any preference or claim to completeness, some of these, all of which have been used by registries in the past for similar transitions, are:
在早期版本的IDNA中，有几种方法可以引入新字符或更改现有字符的映射形式的解释。过渡问题是复杂的，因为IDNA2003中ToUnicode（ToASCII（））翻译后这些标签的形式不仅仍然有效，而且没有提供注册人意图的有力指示：包含“ss”的字符串可能只是该字符串，也可能包含Eszett；包含小写Sigma的字符串可以包含最终Sigma（可以根据字符串中的位置进行启发式猜测，但通过连接单词形成标签的长期传统使此类启发式不可靠），不包含ZWJ或ZWNJ的字符串可能会包含它们。在没有任何偏好或要求完整性的情况下，其中一些（所有这些在过去都被登记处用于类似的过渡）是：
1. Do not permit use of the newly available character at the registry level. This might cause lookup failures if a domain name were to be written with the expectation of the IDNA2003 mapping behavior, but would eliminate any possibility of false matches.
1. 不允许在注册表级别使用新可用的字符。如果域名是按照IDNA2003映射行为编写的，这可能会导致查找失败，但会消除任何错误匹配的可能性。
2. Hold a "sunrise"-like arrangement in which holders of labels containing "ss" in the Eszett case, lowercase Sigma in that case, or that might have contained ZWJ or ZWNJ in context, are given priority (and perhaps other benefits) for registering the corresponding string containing Eszett, Final Sigma, or the appropriate zero-width character respectively.
2. 保持一种类似“日出”的安排，在这种安排中，在Eszett情况下包含“ss”、在该情况下包含小写Sigma、或在上下文中可能包含ZWJ或ZWNJ的标签持有者，在注册包含Eszett、最终Sigma的对应字符串时，被给予优先权（以及可能的其他好处），或相应的零宽度字符。
3. Adopt some sort of "variant" approach in which registrants obtain labels with both character forms.
3. 采用某种“变体”方法，即注册人获得两种字符形式的标签。
4. Adopt a different form of "variant" approach in which registration of additional strings that would produce the same A-label if interpreted according to IDNA2003 is either not permitted at all or permitted only by the registrant who already has one of the names.
4. 采用不同形式的“变体”方法，即如果根据IDNA2003进行解释，则不允许注册产生相同a标签的附加字符串，或者只允许已经拥有其中一个名称的注册人注册。
5. Ignore the issue and assume that the marketplace or other mechanisms will sort things out.
5. 忽略这个问题，假设市场或其他机制会解决问题。
In any event, a registry (at any level of the DNS tree) that chooses to permit labels to be registered that contains these characters, or considers doing so, will have to address the relationship with existing, possibly conflicting, labels in some way, just as
在任何情况下，选择或考虑允许注册包含这些字符的标签的注册表（位于DNS树的任何级别）必须以某种方式解决与现有标签（可能存在冲突）的关系，就像
registries that already had a considerable number of labels did when IDNs were first introduced.
当IDN首次引入时，已经有大量标签的注册中心就已经有了。
As discussed at length in Section 6, IDNA2003, via Nameprep (see Section 7.5), mapped many characters into related ones. Those mappings no longer exist as requirements in IDNA2008. These specifications strongly prefer that only A-labels or U-labels be used in protocol contexts and as much as practical more generally. IDNA2008 does anticipate situations in which some mapping at the time of user input into lookup applications is appropriate and desirable. The issues are discussed in Section 6 and specific recommendations are made in the Mapping document [IDNA2008-Mapping].
正如IDNA2003第6节详细讨论的，通过Nameprep（见第7.5节），将许多字符映射到相关字符中。这些映射不再作为IDNA2008中的需求存在。这些规范强烈建议在协议上下文中仅使用A标签或U标签，并且尽可能更普遍地使用。IDNA2008确实预测了这样的情况，即用户输入到查找应用程序时的一些映射是适当和可取的。第6节讨论了这些问题，并在制图文件[IDNA2008制图]中提出了具体建议。
The conditions that would have required a change in the IDNA ACE prefix ("xn--", used in IDNA2003) were of great concern to the community. A prefix change would have clearly been necessary if the algorithms were modified in a manner that would have created serious ambiguities during subsequent transition in registrations. This section summarizes the working group's conclusions about the conditions under which a change in the prefix would have been necessary and the implications of such a change.
社区非常关注需要更改IDNA ACE前缀（“xn--”，在IDNA2003中使用）的条件。如果算法的修改方式会在随后的注册过渡期间产生严重的歧义，那么前缀更改显然是必要的。本节总结了工作组关于在何种条件下有必要更改前缀以及这种更改的影响的结论。
An IDN prefix change would have been needed if a given string would be looked up or otherwise interpreted differently depending on the version of the protocol or tables being used. This IDNA upgrade would have required a prefix change if, and only if, one of the following four conditions were met:
如果根据所使用的协议或表的版本查找或以其他方式解释给定字符串，则需要更改IDN前缀。如果且仅当满足以下四个条件之一时，此IDNA升级将需要更改前缀：
1. The conversion of an A-label to Unicode (i.e., a U-label) would have yielded one string under IDNA2003 and a different string under IDNA2008.
1. 将A标签转换为Unicode（即U标签）将在IDNA2003下生成一个字符串，在IDNA2008下生成另一个字符串。
2. In a significant number of cases, an input string that was valid under IDNA2003 and also valid under IDNA2008 would have yielded two different A-labels with the different versions. This condition is believed to be essentially equivalent to the one above except for a very small number of edge cases that were not found to justify a prefix change (see Section 7.2).
2. 在很多情况下，一个在IDNA2003和IDNA2008下都有效的输入字符串会产生两个不同版本的a标签。这种情况被认为基本上等同于上述情况，除了极少数边缘情况无法证明前缀更改的合理性（见第7.2节）。
Note that if the input string was valid under one version and not valid under the other, this condition would not apply. See the first item in Section 7.4.2, below.
请注意，如果输入字符串在一个版本下有效，而在另一个版本下无效，则此条件将不适用。见下文第7.4.2节中的第一项。
3. A fundamental change was made to the semantics of the string that would be inserted in the DNS, e.g., if a decision were made to try to include language or script information in the encoding in addition to the string itself.
3. 对将插入DNS中的字符串的语义进行了根本性更改，例如，如果决定尝试在编码中除了字符串本身之外还包括语言或脚本信息。
4. A sufficiently large number of characters were added to Unicode so that the Punycode mechanism for block offsets would no longer reference the higher-numbered planes and blocks. This condition is unlikely even in the long term and certain not to arise in the next several years.
4. 在Unicode中添加了足够多的字符，以便块偏移的Punycode机制不再引用编号较高的平面和块。这种情况即使在长期内也不太可能出现，而且在未来几年内肯定不会出现。
As a result of the principles described above, none of the following changes required a new prefix:
根据上述原则，以下任何更改都不需要新前缀：
1. Prohibition of some characters as input to IDNA. Such a prohibition might make names that were previously registered inaccessible, but did not change those names.
1. 禁止某些字符作为IDNA的输入。这种禁止可能会使以前注册的名称无法访问，但不会更改这些名称。
2. Adjustments in IDNA tables or actions, including normalization definitions, that affected characters that were already invalid under IDNA2003.
2. IDNA表或操作中的调整，包括规范化定义，影响了IDNA2003下已经无效的字符。
3. Changes in the style of the IDNA definition that did not alter the actions performed by IDNA.
3. IDNA定义样式的更改，不会改变IDNA执行的操作。
While it might have been possible to make a prefix change, the costs of such a change are considerable. Registries could not have converted all IDNA2003 ("xn--") registrations to a new form at the same time and synchronize that change with applications supporting lookup. Unless all existing registrations were simply to be declared invalid (and perhaps even then), systems that needed to support both labels with old prefixes and labels with new ones would be required to first process a putative label under the IDNA2008 rules and try to look it up and then, if it were not found, would be required to process the label under IDNA2003 rules and look it up again. That process would probably have significantly slowed down all processing that involved IDNs in the DNS, especially since a fully-qualified name might contain a mixture of labels that were registered with the old and new prefixes. That would have made DNS caching very difficult. In addition, looking up the same input string as two separate A-labels would have created some potential for confusion and attacks, since the labels could map to different targets and then resolve to different entries in the DNS.
虽然可能会对前缀进行更改，但这种更改的成本是相当大的。注册表不可能同时将所有IDNA2003（“xn--”）注册转换为新表单，并将该更改与支持查找的应用程序同步。除非所有现有注册被简单地宣布为无效（甚至可能是无效），否则需要同时支持带有旧前缀的标签和带有新前缀的标签的系统将被要求首先根据IDNA2008规则处理一个假定的标签，并尝试查找它，如果没有找到它，将需要根据IDNA2003规则处理标签并再次查找。这一过程可能会大大降低DNS中涉及IDN的所有处理速度，特别是因为完全限定名称可能包含使用新旧前缀注册的混合标签。这将使DNS缓存变得非常困难。此外，查找同一输入字符串作为两个单独的A标签可能会造成混淆和攻击，因为标签可能映射到不同的目标，然后解析到DNS中的不同条目。
Consequently, a prefix change should have been, and was, avoided if at all possible, even if it means accepting some IDNA2003 decisions about character distinctions as irreversible and/or giving special treatment to edge cases.
因此，如果可能的话，前缀更改本来应该避免，也曾经避免，即使这意味着接受IDNA2003关于字符区分的一些决定，认为是不可逆转的和/或对边缘情况给予特殊处理。
The Nameprep specification [RFC3491], a key part of IDNA2003, is a profile of Stringprep [RFC3454]. While Nameprep is a Stringprep profile specific to IDNA, Stringprep is used by a number of other protocols. Were Stringprep to have been modified by IDNA2008, those changes to improve the handling of IDNs could cause problems for non-DNS uses, most notably if they affected identification and authentication protocols. Several elements of IDNA2008 give interpretations to strings prohibited under IDNA2003 or prohibit strings that IDNA2003 permitted. Those elements include the new inclusion information in the Tables document [RFC5892], the reduction in the number of characters permitted as input for registration or lookup (Section 3), and even the changes in handling of right-to-left strings as described in the Bidi document [RFC5893]. IDNA2008 does not use Nameprep or Stringprep at all, so there are no side-effect changes to other protocols.
Nameprep规范[RFC3491]是IDNA2003的关键部分，是Stringprep[RFC3454]的概要文件。虽然Nameprep是IDNA特有的Stringprep配置文件，但Stringprep被许多其他协议使用。如果Stringprep已被IDNA2008修改，则这些改进IDN处理的更改可能会导致非DNS使用出现问题，尤其是如果它们影响了标识和身份验证协议。IDNA2008的几个元素对IDNA2003禁止的字符串或IDNA2003允许的禁止字符串进行了解释。这些元素包括表格文档[RFC5892]中的新包含信息、注册或查找时允许输入的字符数的减少（第3节），甚至Bidi文档[RFC5893]中描述的从右向左字符串处理的变化。IDNA2008根本不使用Nameprep或Stringprep，因此对其他协议没有任何副作用更改。
It is particularly important to keep IDNA processing separate from processing for various security protocols because some of the constraints that are necessary for smooth and comprehensible use of IDNs may be unwanted or undesirable in other contexts. For example, the criteria for good passwords or passphrases are very different from those for desirable IDNs: passwords should be hard to guess, while domain names should normally be easily memorable. Similarly, internationalized Small Computer System Interface (SCSI) identifiers and other protocol components are likely to have different requirements than IDNs.
将IDNA处理与各种安全协议的处理分开是特别重要的，因为在其他上下文中，顺利和可理解地使用IDN所必需的一些约束可能是不需要的或不需要的。例如，好的密码或密码短语的标准与理想的IDN的标准非常不同：密码应该很难猜测，而域名通常应该很容易记住。类似地，国际化小型计算机系统接口（SCSI）标识符和其他协议组件可能与IDN有不同的要求。
One of the major differences between this specification and the original version of IDNA is that IDNA2003 permitted non-letter symbols of various sorts, including punctuation and line-drawing symbols, in the protocol. They were always discouraged in practice. In particular, both the "IESG Statement" about IDNA and all versions of the ICANN Guidelines specify that only language characters be used in labels. This specification disallows symbols entirely. There are several reasons for this, which include:
本规范与IDNA原始版本之间的主要区别之一是，IDNA2003允许协议中使用各种非字母符号，包括标点符号和划线符号。他们在实践中总是感到气馁。特别是，关于IDNA的“IESG声明”和ICANN指南的所有版本都规定标签中只能使用语言字符。本规范完全不允许使用符号。这有几个原因，其中包括：
1. As discussed elsewhere, the original IDNA specification assumed that as many Unicode characters as possible should be permitted, directly or via mapping to other characters, in IDNs. This
1. 正如其他地方所讨论的，最初的IDNA规范假设在IDN中应该直接或通过映射到其他字符来允许尽可能多的Unicode字符。这
specification operates on an inclusion model, extrapolating from the original "hostname" rules (LDH, see the Definitions document [RFC5890]) -- which have served the Internet very well -- to a Unicode base rather than an ASCII base.
该规范以包含模型为基础，从最初的“主机名”规则（LDH，请参阅定义文档[RFC5890]）推演到Unicode基础，而不是ASCII基础。
2. Symbol names are more problematic than letters because there may be no general agreement on whether a particular glyph matches a symbol; there are no uniform conventions for naming; variations such as outline, solid, and shaded forms may or may not exist; and so on. As just one example, consider a "heart" symbol as it might appear in a logo that might be read as "I love...". While the user might read such a logo as "I love..." or "I heart...", considerable knowledge of the coding distinctions made in Unicode is needed to know that there is more than one "heart" character (e.g., U+2665, U+2661, and U+2765) and how to describe it. These issues are of particular importance if strings are expected to be understood or transcribed by the listener after being read out loud.
2. 符号名称的问题比字母更大，因为对于某个符号是否与某个符号匹配，可能没有普遍的一致意见；命名没有统一的约定；轮廓、实体和阴影形式等变化可能存在，也可能不存在；等等作为一个例子，考虑一个“心”的符号，因为它可能出现在一个标志中，可以被称为“我爱…”。虽然用户可能会阅读诸如“我爱…”或“我的心…”之类的徽标，但需要相当多的Unicode编码区别知识才能知道有多个“心”字符（例如U+2665、U+2661和U+2765）以及如何描述它。如果希望听者在大声朗读后理解或转录字符串，则这些问题尤为重要。
3. Design of a screen reader used by blind Internet users who must listen to renderings of IDN domain names and possibly reproduce them on the keyboard becomes considerably more complicated when the names of characters are not obvious and intuitive to anyone familiar with the language in question.
3. 盲人互联网用户使用的屏幕阅读器的设计变得相当复杂，他们必须听IDN域名的渲染，并可能在键盘上重现这些渲染。当熟悉该语言的人看不到字符的名称时，屏幕阅读器的设计就变得相当复杂。
4. As a simplified example of this, assume one wanted to use a "heart" or "star" symbol in a label. This is problematic because those names are ambiguous in the Unicode system of naming (the actual Unicode names require far more qualification). A user or would-be registrant has no way to know -- absent careful study of the code tables -- whether it is ambiguous (e.g., where there are multiple "heart" characters) or not. Conversely, the user seeing the hypothetical label doesn't know whether to read it -- try to transmit it to a colleague by voice -- as "heart", as "love", as "black heart", or as any of the other examples below.
4. 作为一个简化的例子，假设一个人想要在标签中使用“心”或“星”符号。这是有问题的，因为这些名称在Unicode命名系统中是不明确的（实际的Unicode名称需要更多的限定）。如果不仔细研究代码表，用户或潜在注册者无法知道代码表是否含糊不清（例如，有多个“心脏”字符）。相反，看到假想标签的用户不知道是否要阅读它——试着通过语音将其传送给同事——作为“心”、“爱”、“黑心”或下面的任何其他示例。
5. The actual situation is even worse than this. There is no possible way for a normal, casual, user to tell the difference between the hearts of U+2665 and U+2765 and the stars of U+2606 and U+2729 without somehow knowing to look for a distinction. We have a white heart (U+2661) and few black hearts. Consequently, describing a label as containing a heart is hopelessly ambiguous: we can only know that it contains one of several characters that look like hearts or have "heart" in their names. In cities where "Square" is a popular part of a location name, one might well want to use a square symbol in a label as well and there are far more squares of various flavors in Unicode than there are hearts or stars.
5. 实际情况甚至比这更糟。对于一个普通、随意的用户来说，如果不知道如何寻找区别，就不可能分辨出U+2665和U+2765的心脏与U+2606和U+2729的星星之间的区别。我们有一颗白心（U+2661）和几个黑心。因此，将一个标签描述为包含一颗心是毫无疑问的模棱两可：我们只能知道它包含几个看起来像心或名称中有“心”的字符之一。在城市中，“正方形”是位置名称的一个流行部分，人们可能也希望在标签中使用正方形符号，而且Unicode中的各种风格的正方形远多于红心或星星。
The consequence of these ambiguities is that symbols are a very poor basis for reliable communication. Consistent with this conclusion, the Unicode standard recommends that strings used in identifiers not contain symbols or punctuation [Unicode-UAX31]. Of course, these difficulties with symbols do not arise with actual pictographic languages and scripts which would be treated like any other language characters; the two should not be confused.
这些模棱两可的结果是，符号是可靠通信的一个非常差的基础。与此结论一致，Unicode标准建议标识符中使用的字符串不包含符号或标点符号[Unicode-UAX31]。当然，这些符号上的困难并不会出现在实际的象形文字和文字上，因为象形文字和文字会被视为其他语言文字；两者不应混淆。
In IDNA2003, labels containing unassigned code points are looked up on the assumption that, if they appear in labels and can be mapped and then resolved, the relevant standards must have changed and the registry has properly allocated only assigned values.
在IDNA2003中，如果包含未分配代码点的标签出现在标签中，并且可以映射然后解析，则相关标准必须已更改，并且注册表仅正确分配了分配值，则会根据这一假设来查找这些标签。
In the IDNA2008 protocol, strings containing unassigned code points must not be either looked up or registered. In summary, the status of an unassigned character with regard to the DISALLOWED, PROTOCOL-VALID, and CONTEXTUAL RULE REQUIRED categories cannot be evaluated until a character is actually assigned and known. There are several reasons for this, with the most important ones being:
在IDNA2008协议中，不能查找或注册包含未分配代码点的字符串。总之，在实际分配和已知字符之前，无法评估未分配字符在不允许、协议有效和上下文规则必需类别中的状态。这有几个原因，其中最重要的是：
o Tests involving the context of characters (e.g., some characters being permitted only adjacent to others of specific types) and integrity tests on complete labels are needed. Unassigned code points cannot be permitted because one cannot determine whether particular code points will require contextual rules (and what those rules should be) before characters are assigned to them and the properties of those characters fully understood.
o 需要进行涉及字符上下文的测试（例如，某些字符仅允许与其他特定类型的字符相邻）以及完整标签的完整性测试。不允许使用未分配的代码点，因为在向特定代码点分配字符并完全理解这些字符的属性之前，无法确定特定代码点是否需要上下文规则（以及这些规则应该是什么）。
o It cannot be known in advance, and with sufficient reliability, whether a newly assigned code point will be associated with a character that would be disallowed by the rules in the Tables document [RFC5892] (such as a compatibility character). In IDNA2003, since there is no direct dependency on NFKC (many of the entries in Stringprep's tables are based on NFKC, but IDNA2003 depends only on Stringprep), allocation of a compatibility character might produce some odd situations, but it would not be a problem. In IDNA2008, where compatibility characters are DISALLOWED unless character-specific exceptions are made, permitting strings containing unassigned characters to be looked up would violate the principle that characters in DISALLOWED are not looked up.
o 无法预先知道新分配的代码点是否与表文档[RFC5892]中的规则不允许的字符（例如兼容字符）关联，并且具有足够的可靠性。在IDNA2003中，由于没有对NFKC的直接依赖（Stringprep表中的许多条目都基于NFKC，但IDNA2003仅依赖于Stringprep），因此兼容性字符的分配可能会产生一些奇怪的情况，但这不会是问题。在IDNA2008中，除非出现特定于字符的例外情况，否则不允许使用兼容字符，允许查找包含未分配字符的字符串将违反不允许使用的字符不被查找的原则。
o The Unicode Standard specifies that an unassigned code point normalizes (and, where relevant, case folds) to itself. If the code point is later assigned to a character, and particularly if the newly assigned code point has a combining class that
o Unicode标准规定未分配的代码点将自身规范化（以及在相关情况下，大小写折叠）。如果稍后将代码点指定给字符，尤其是如果新指定的代码点具有以下组合类：
determines its placement relative to other combining characters, it could normalize to some other code point or sequence.
确定其相对于其他组合字符的位置，它可以规范化为其他代码点或序列。
It is possible to argue that the issues above are not important and that, as a consequence, it is better to retain the principle of looking up labels even if they contain unassigned characters because all of the important scripts and characters have been coded as of Unicode 5.2 (or even earlier), and hence unassigned code points will be assigned only to obscure characters or archaic scripts. Unfortunately, that does not appear to be a safe assumption for at least two reasons. First, much the same claim of completeness has been made for earlier versions of Unicode. The reality is that a script that is obscure to much of the world may still be very important to those who use it. Cultural and linguistic preservation principles make it inappropriate to declare the script of no importance in IDNs. Second, we already have counterexamples, e.g., in the relationships associated with new Han characters being added (whether in the BMP or in Unicode Plane 2).
有可能认为上述问题并不重要，因此，最好保留查找标签的原则，即使标签包含未分配的字符，因为所有重要的脚本和字符都是在Unicode 5.2（或更早）时编码的，因此，未分配的代码点将只分配给晦涩的字符或古老的脚本。不幸的是，这似乎不是一个安全的假设，至少有两个原因。首先，对于Unicode的早期版本，也有很多相同的完整性声明。现实情况是，一个对世界上很多人来说都不太清楚的脚本对那些使用它的人来说可能仍然非常重要。文化和语言保护原则使得在IDN中声明脚本不重要是不合适的。其次，我们已经有了反例，例如，在与正在添加的新汉字相关联的关系中（无论是在BMP中还是在Unicode平面2中）。
Independent of the technical transition issues identified above, it can be observed that any addition of characters to an existing script to make it easier to use or to better accommodate particular languages may lead to transition issues. Such additions may change the preferred form for writing a particular string, changes that may be reflected, e.g., in keyboard transition modules that would necessarily be different from those for earlier versions of Unicode where the newer characters may not exist. This creates an inherent transition problem because attempts to access labels may use either the old or the new conventions, requiring registry action whether or not the older conventions were used in labels. The need to consider transition mechanisms is inherent to evolution of Unicode to better accommodate writing systems and is independent of how IDNs are represented in the DNS or how transitions among versions of those mechanisms occur. The requirement for transitions of this type is illustrated by the addition of Malayalam Chillu in Unicode 5.1.0.
与上面确定的技术转换问题无关，可以观察到，在现有脚本中添加字符以使其更易于使用或更好地适应特定语言可能会导致转换问题。这样的添加可能会改变写入特定字符串的首选形式，这些变化可能会反映在键盘转换模块中，例如，键盘转换模块必然不同于早期版本的Unicode（其中可能不存在较新的字符）。这会产生固有的转换问题，因为访问标签的尝试可能使用旧的或新的约定，无论标签中是否使用旧的约定，都需要注册表操作。需要考虑转换机制是Unicode的演进所固有的，以便更好地适应写入系统，并且独立于DNS在DNS中如何表示，或者如何发生这些机制的版本之间的转换。通过在Unicode 5.1.0中添加Malayalam Chillu来说明这种类型转换的要求。
The 2003 IDNA model includes several odd artifacts of the context in which it was developed. Many, if not all, of these are potential avenues for exploits, especially if the registration process permits "source" names (names that have not been processed through IDNA and Nameprep) to be registered. As one example, since the character Eszett, used in German, is mapped by IDNA2003 into the sequence "ss" rather than being retained as itself or prohibited, a string containing that character, but that is otherwise in ASCII, is not really an IDN (in the U-label sense defined above). After Nameprep maps out the Eszett, the result is an ASCII string and so it does not
2003年的IDNA模型包含了它开发环境中的几个奇怪的工件。其中许多（如果不是全部的话）是潜在的漏洞利用途径，特别是如果注册过程允许注册“源”名称（未通过IDNA和Nameprep处理的名称）。例如，由于德语中使用的字符Eszett由IDNA2003映射到序列“ss”中，而不是保留为其本身或被禁止，因此包含该字符的字符串（但在其他情况下为ASCII格式）实际上不是IDN（在上面定义的U标签意义下）。在Nameprep映射出Eszett之后，结果是一个ASCII字符串，因此它不是
get an xn-- prefix, but the string that can be displayed to a user appears to be an IDN. IDNA2008 eliminates this artifact. A character is either permitted as itself or it is prohibited; special cases that make sense only in a particular linguistic or cultural context can be dealt with as localization matters where appropriate.
获取xn--前缀，但可以显示给用户的字符串似乎是IDN。IDNA2008消除了这个工件。一个字符要么被允许作为其本身，要么被禁止；只有在特定的语言或文化背景下才有意义的特殊情况，可以在适当的情况下作为本地化问题处理。
Existing DNS servers do not know the IDNA rules for handling non-ASCII forms of IDNs, and therefore need to be shielded from them. All existing channels through which names can enter a DNS server database (for example, master files (as described in RFC 1034) and DNS update messages [RFC2136]) could not be IDNA-aware because they predate IDNA. Other sections of this document provide the needed shielding by ensuring that internationalized domain names entering DNS server databases through such channels have already been converted to their equivalent ASCII A-label forms.
现有DNS服务器不知道处理非ASCII形式IDN的IDNA规则，因此需要屏蔽这些规则。名称可以通过其进入DNS服务器数据库的所有现有通道（例如，主文件（如RFC 1034中所述）和DNS更新消息[RFC2136]）都不能识别IDNA，因为它们早于IDNA。本文档的其他部分通过确保通过此类通道进入DNS服务器数据库的国际化域名已转换为其等效的ASCII A标签形式，提供了所需的屏蔽。
Because of the distinction made between the algorithms for Registration and Lookup in Sections 4 and 5 (respectively) of the Protocol document [RFC5891] (a domain name containing only ASCII code points cannot be converted to an A-label), there cannot be more than one A-label form for any given U-label.
由于协议文件[RFC5891]第4节和第5节（分别）对注册和查找算法进行了区分（仅包含ASCII码点的域名不能转换为a标签），任何给定U标签的a标签形式不得超过一个。
As specified in clarifications to the DNS specification [RFC2181], the DNS protocol explicitly allows domain labels to contain octets beyond the ASCII range (0000..007F), and this document does not change that. However, although the interpretation of octets 0080..00FF is well-defined in the DNS, many application protocols support only ASCII labels and there is no defined interpretation of these non-ASCII octets as characters and, in particular, no interpretation of case-independent matching for them (e.g., see the clarification on DNS case insensitivity [RFC4343]). If labels containing these octets are returned to applications, unpredictable behavior could result. The A-label form, which cannot contain those characters, is the only standard representation for internationalized labels in the DNS protocol.
如DNS规范澄清[RFC2181]中所述，DNS协议明确允许域标签包含超出ASCII范围（0000..007F）的八位字节，本文档不改变这一点。然而，尽管八位字节0080..00FF的解释在DNS中有很好的定义，但许多应用程序协议仅支持ASCII标签，并且没有将这些非ASCII八位字节定义为字符的解释，特别是，没有解释它们的大小写无关匹配（例如，请参阅DNS大小写不敏感的说明）[RFC4343]）。如果将包含这些八位字节的标签返回给应用程序，可能会导致不可预测的行为。不能包含这些字符的A标签表单是DNS协议中国际化标签的唯一标准表示形式。
IDNs in A-label form will generally be somewhat longer than current domain names, so the bandwidth needed by the root servers is likely to go up by a small amount. Also, queries and responses for IDNs will probably be somewhat longer than typical queries historically,
A标签形式的IDN通常比当前域名稍长，因此根服务器所需的带宽可能会小幅增加。此外，IDN的查询和响应可能比以往的典型查询要长一些，
so Extension Mechanisms for DNS (EDNS0) [RFC2671] support may be more important (otherwise, queries and responses may be forced to go to TCP instead of UDP).
因此，DNS（EDNS0）[RFC2671]支持的扩展机制可能更为重要（否则，查询和响应可能会被迫转到TCP而不是UDP）。
DNS labels and fully-qualified domain names provide mnemonics that assist in identifying and referring to resources on the Internet. IDNs expand the range of those mnemonics to include those based on languages and character sets other than Western European and Roman-derived ones. But domain "names" are not, in general, words in any language. The recommendations of the IETF policy on character sets and languages (BCP 18 [RFC2277]) are applicable to situations in which language identification is used to provide language-specific contexts. The DNS is, by contrast, global and international and ultimately has nothing to do with languages. Adding languages (or similar context) to IDNs generally, or to DNS matching in particular, would imply context-dependent matching in DNS, which would be a very significant change to the DNS protocol itself. It would also imply that users would need to identify the language associated with a particular label in order to look that label up. That knowledge is generally not available because many labels are not words in any language and some may be words in more than one.
DNS标签和完全限定的域名提供帮助识别和引用Internet上资源的助记符。IDN扩展了这些助记符的范围，包括那些基于语言和字符集的助记符，而不是西欧和罗马派生的助记符。但域名通常不是任何语言中的单词。IETF字符集和语言政策（BCP 18[RFC2277]）的建议适用于使用语言标识提供特定语言上下文的情况。相比之下，DNS是全球性和国际性的，最终与语言无关。将语言（或类似上下文）添加到IDN中，或者特别添加到DNS匹配中，将意味着DNS中的上下文相关匹配，这将是对DNS协议本身的一个非常重要的更改。这还意味着用户需要识别与特定标签相关联的语言，以便查找该标签。这种知识通常是不可用的，因为许多标签不是任何语言中的单词，有些可能是多个语言中的单词。
This section gives an overview of IANA registries required for IDNA. The actual definitions of, and specifications for, the first two, which have been newly created for IDNA2008, appear in the Tables document [RFC5892]. This document describes the registries, but it does not specify any IANA actions.
本节概述了IDNA所需的IANA注册中心。为IDNA2008新创建的前两个的实际定义和规范见表格文档[RFC5892]。本文档描述了注册表，但未指定任何IANA操作。
The distinction among the major categories "UNASSIGNED", "DISALLOWED", "PROTOCOL-VALID", and "CONTEXTUAL RULE REQUIRED" is made by special categories and rules that are integral elements of the Tables document. While not normative, an IANA registry of characters and scripts and their categories, updated for each new version of Unicode and the characters it contains, are convenient for programming and validation purposes. The details of this registry are specified in the Tables document.
主要类别“未分配”、“不允许”、“协议有效”和“所需上下文规则”之间的区别由作为表格文档组成部分的特殊类别和规则来确定。虽然不是规范性的，但字符和脚本及其类别的IANA注册表（针对每个新版本的Unicode及其包含的字符进行更新）便于编程和验证。此注册表的详细信息在Tables文档中指定。
IANA has created and now maintains a list of approved contextual rules for characters that are defined in the IDNA Character Registry list as requiring a Contextual Rule (i.e., the types of rules described in Section 3.1.2). The details for those rules appear in the Tables document.
IANA已经为IDNA字符注册列表中定义为需要上下文规则的字符（即第3.1.2节中描述的规则类型）创建并维护了一个已批准的上下文规则列表。这些规则的详细信息将显示在Tables文档中。
This registry, historically described as the "IANA Language Character Set Registry" or "IANA Script Registry" (both somewhat misleading terms), is maintained by IANA at the request of ICANN. It is used to provide a central documentation repository of the IDN policies used by top level domain (TLD) registries who volunteer to contribute to it and is used in conjunction with ICANN Guidelines for IDN use.
该注册中心历史上被称为“IANA语言字符集注册中心”或“IANA脚本注册中心”（这两个术语都有点误导性），由IANA应ICANN的要求进行维护。它用于提供顶级域（TLD）注册机构自愿参与的IDN策略的中央文档存储库，并与ICANN IDN使用指南结合使用。
It is not an IETF-managed registry and, while the protocol changes specified here may call for some revisions to the tables, IDNA2008 has no direct effect on that registry and no IANA action is required as a result.
它不是IETF管理的注册表，虽然此处指定的协议更改可能需要对表进行一些修订，但IDNA2008对该注册表没有直接影响，因此不需要IANA操作。
This document is purely explanatory and informational and consequently introduces no new security issues. It would, of course, be a poor idea for someone to try to implement from it; such an attempt would almost certainly lead to interoperability problems and might lead to security ones. A discussion of security issues with IDNA, including some relevant history, appears in the Definitions document [RFC5890].
本文档纯粹是解释性和信息性的，因此不会引入新的安全问题。当然，如果有人试图从中实施，那将是一个糟糕的想法；这样的尝试几乎肯定会导致互操作性问题，并可能导致安全问题。关于IDNA安全问题的讨论，包括一些相关历史记录，见定义文档[RFC5890]。
The editor and contributors would like to express their thanks to those who contributed significant early (pre-working group) review comments, sometimes accompanied by text, Paul Hoffman, Simon Josefsson, and Sam Weiler. In addition, some specific ideas were incorporated from suggestions, text, or comments about sections that were unclear supplied by Vint Cerf, Frank Ellerman, Michael Everson, Asmus Freytag, Erik van der Poel, Michel Suignard, and Ken Whistler. Thanks are also due to Vint Cerf, Lisa Dusseault, Debbie Garside, and Jefsey Morfin for conversations that led to considerable improvements in the content of this document and to several others, including Ben
编辑和撰稿人要向那些提供重要早期（工作组前期）评论意见的人表示感谢，这些评论有时还附有文本、保罗·霍夫曼（Paul Hoffman）、西蒙·约瑟夫森（Simon Josefsson）和山姆·韦勒（Sam Weiler）。此外，从文特·瑟夫、弗兰克·埃勒曼、迈克尔·埃弗森、阿斯穆斯·弗雷塔格、埃里克·范德波尔、米歇尔·苏伊格纳德和肯·惠斯勒提供的关于不明确章节的建议、文本或评论中纳入了一些具体想法。感谢Vint Cerf、Lisa Dusseault、Debbie Garside和Jefsey Morfin的对话，这些对话使本文档的内容有了很大的改进，也感谢其他人，包括Ben
Campbell, Martin Duerst, Subramanian Moonesamy, Peter Saint-Andre, and Dan Winship, for catching specific errors and recommending corrections.
Campbell、Martin Duerst、Subramanian Moonesay、Peter Saint Andre和Dan Winship，用于捕捉特定错误并建议更正。
A meeting was held on 30 January 2008 to attempt to reconcile differences in perspective and terminology about this set of specifications between the design team and members of the Unicode Technical Consortium. The discussions at and subsequent to that meeting were very helpful in focusing the issues and in refining the specifications. The active participants at that meeting were (in alphabetic order, as usual) Harald Alvestrand, Vint Cerf, Tina Dam, Mark Davis, Lisa Dusseault, Patrik Faltstrom (by telephone), Cary Karp, John Klensin, Warren Kumari, Lisa Moore, Erik van der Poel, Michel Suignard, and Ken Whistler. We express our thanks to Google for support of that meeting and to the participants for their contributions.
2008年1月30日举行了一次会议，试图调和设计团队和Unicode技术联盟成员之间在这套规范的角度和术语方面的差异。该次会议及其后的讨论非常有助于集中讨论问题和完善规范。这次会议的积极参与者（按字母顺序，一如既往）有哈拉尔·阿尔韦斯特朗、温特·瑟夫、蒂娜·达姆、马克·戴维斯、丽莎·杜肖奥、帕特里克·法茨特罗姆（通过电话）、卡里·卡普、约翰·克莱辛、沃伦·库马里、丽莎·摩尔、埃里克·范德波尔、米歇尔·苏伊纳尔和肯·惠斯勒。我们感谢谷歌对这次会议的支持，感谢与会者的贡献。
Useful comments and text on the working group versions of the working draft were received from many participants in the IETF "IDNABIS" working group and a number of document changes resulted from mailing list discussions made by that group. Marcos Sanz provided specific analysis and suggestions that were exceptionally helpful in refining the text, as did Vint Cerf, Martin Duerst, Andrew Sullivan, and Ken Whistler. Lisa Dusseault provided extensive editorial suggestions during the spring of 2009, most of which were incorporated.
IETF“IDNABIS”工作组的许多参与者对工作组版本的工作草案提出了有用的意见和文本，该工作组的邮件列表讨论导致了一些文件更改。马科斯·桑兹（Marcos Sanz）提供了特别有用的具体分析和建议，文特·瑟夫（Vint Cerf）、马丁·杜尔斯特（Martin Duerst）、安德鲁·沙利文（Andrew Sullivan）和肯·惠斯勒（Ken Whistler）也提供了这些分析和建议。Lisa Dusseault在2009年春季提供了广泛的编辑建议，其中大部分被合并。
While the listed editor held the pen, the core of this document and the initial working group version represents the joint work and conclusions of an ad hoc design team consisting of the editor and, in alphabetic order, Harald Alvestrand, Tina Dam, Patrik Faltstrom, and Cary Karp. Considerable material describing mapping principles has been incorporated from a draft of the Mapping document [IDNA2008-Mapping] by Pete Resnick and Paul Hoffman. In addition, there were many specific contributions and helpful comments from those listed in the Acknowledgments section and others who have contributed to the development and use of the IDNA protocols.
虽然列出的编辑手握笔，但本文件的核心和工作组的初始版本代表了一个特设设计团队的共同工作和结论，该团队由编辑以及按字母顺序排列的Harald Alvestrand、Tina Dam、Patrik Faltstrom和Cary Karp组成。彼得·雷斯尼克（Pete Resnick）和保罗·霍夫曼（Paul Hoffman）的测绘文件[IDNA2008测绘]草稿中包含了大量描述测绘原则的材料。此外，感谢部分所列人员以及其他对IDNA协议的开发和使用做出贡献的人员也做出了许多具体贡献和有益评论。
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003.
[RFC3490]Faltstrom，P.，Hoffman，P.，和A.Costello，“应用程序中的域名国际化（IDNA）”，RFC 34902003年3月。
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode for Internationalized Domain Names in Applications (IDNA)", RFC 3492, March 2003.
[RFC3492]Costello，A.，“Punycode：应用程序中国际化域名的Unicode引导字符串编码（IDNA）”，RFC 3492，2003年3月。
[RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, August 2010.
[RFC5890]Klensin，J.，“应用程序的国际化域名（IDNA）：定义和文档框架”，RFC 58902010年8月。
[RFC5891] Klensin, J., "Internationalized Domain Names in Applications (IDNA): Protocol", RFC 5891, August 2010.
[RFC5891]Klensin，J.，“应用程序中的国际化域名（IDNA）：协议”，RFC 58912010年8月。
[RFC5892] Faltstrom, P., "The Unicode Code Points and Internationalized Domain Names for Applications (IDNA)", RFC 5892, August 2010.
[RFC5892]Faltstrom，P.，“Unicode代码点和应用程序的国际化域名（IDNA）”，RFC 58922010年8月。
[RFC5893] Alvestrand, H. and C. Karp, "Right-to-Left Scripts for Internationalized Domain Names for Applications (IDNA)", RFC 5893, August 2010.
[RFC5893]Alvestrand，H.和C.Karp，“应用程序国际化域名（IDNA）的从右到左脚本”，RFC 58932010年8月。
[Unicode52] The Unicode Consortium. The Unicode Standard, Version 5.2.0, defined by: "The Unicode Standard, Version 5.2.0", (Mountain View, CA: The Unicode Consortium, 2009. ISBN 978-1-936213-00-9). <http://www.unicode.org/versions/Unicode5.2.0/>.
[Unicode 52]Unicode联盟。Unicode标准，版本5.2.0，定义为：“Unicode标准，版本5.2.0”（加利福尼亚州山景城：Unicode联盟，2009年。ISBN 978-1-936213-00-9）<http://www.unicode.org/versions/Unicode5.2.0/>.
[IDNA2008-Mapping] Resnick, P. and P. Hoffman, "Mapping Characters in Internationalized Domain Names for Applications (IDNA)", Work in Progress, April 2010.
[IDNA2008映射]Resnick，P.和P.Hoffman，“应用程序国际化域名（IDNA）中的字符映射”，正在进行的工作，2010年4月。
[RFC0952] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet host table specification", RFC 952, October 1985.
[RFC0952]Harrenstien，K.，Stahl，M.和E.Feinler，“国防部互联网主机表规范”，RFC 952，1985年10月。
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987.
[RFC1034]Mockapetris，P.，“域名-概念和设施”，STD 13，RFC 1034，1987年11月。
[RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987.
[RFC1035]Mockapetris，P.，“域名-实现和规范”，STD 13，RFC 1035，1987年11月。
[RFC1123] Braden, R., "Requirements for Internet Hosts - Application and Support", STD 3, RFC 1123, October 1989.
[RFC1123]Braden，R.，“互联网主机的要求-应用和支持”，STD 3，RFC 1123，1989年10月。
[RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997.
[RFC2136]Vixie，P.，Thomson，S.，Rekhter，Y.，和J.Bound，“域名系统中的动态更新（DNS更新）”，RFC 21361997年4月。
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS Specification", RFC 2181, July 1997.
[RFC2181]Elz，R.和R.Bush，“DNS规范的澄清”，RFC 21811997年7月。
[RFC2277] Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, January 1998.
[RFC2277]Alvestrand，H.，“IETF字符集和语言政策”，BCP 18，RFC 2277，1998年1月。
[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671, August 1999.
[RFC2671]Vixie，P.，“DNS的扩展机制（EDNS0）”，RFC 26711999年8月。
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000.
[RFC2782]Gulbrandsen，A.，Vixie，P.和L.Esibov，“用于指定服务位置（DNS SRV）的DNS RR”，RFC 2782，2000年2月。
[RFC3454] Hoffman, P. and M. Blanchet, "Preparation of Internationalized Strings ("stringprep")", RFC 3454, December 2002.
[RFC3454]Hoffman，P.和M.Blanchet，“国际化弦的准备（“stringprep”）”，RFC 3454，2002年12月。
[RFC3491] Hoffman, P. and M. Blanchet, "Nameprep: A Stringprep Profile for Internationalized Domain Names (IDN)", RFC 3491, March 2003.
[RFC3491]Hoffman，P.和M.Blanchet，“Nameprep：国际化域名（IDN）的Stringprep配置文件”，RFC 3491，2003年3月。
[RFC3743] Konishi, K., Huang, K., Qian, H., and Y. Ko, "Joint Engineering Team (JET) Guidelines for Internationalized Domain Names (IDN) Registration and Administration for Chinese, Japanese, and Korean", RFC 3743, April 2004.
[RFC3743]Konishi，K.，Huang，K.，Qian，H.，和Y.Ko，“中国，日本和韩国的国际域名（IDN）注册和管理联合工程团队（JET）指南”，RFC 37432004年4月。
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, January 2005.
[RFC3987]Duerst，M.和M.Suignard，“国际化资源标识符（IRIs）”，RFC 3987，2005年1月。
[RFC4290] Klensin, J., "Suggested Practices for Registration of Internationalized Domain Names (IDN)", RFC 4290, December 2005.
[RFC4290]Klensin，J.，“国际域名（IDN）注册的建议做法”，RFC 42902005年12月。
[RFC4343] Eastlake, D., "Domain Name System (DNS) Case Insensitivity Clarification", RFC 4343, January 2006.
[RFC4343]Eastlake，D.，“域名系统（DNS）案例不敏感澄清”，RFC 4343，2006年1月。
[RFC4690] Klensin, J., Faltstrom, P., Karp, C., and IAB, "Review and Recommendations for Internationalized Domain Names (IDNs)", RFC 4690, September 2006.
[RFC4690]Klensin，J.，Faltstrom，P.，Karp，C.，和IAB，“国际化域名（IDN）的审查和建议”，RFC 46902006年9月。
[RFC4713] Lee, X., Mao, W., Chen, E., Hsu, N., and J. Klensin, "Registration and Administration Recommendations for Chinese Domain Names", RFC 4713, October 2006.
[RFC4713]Lee，X.，Mao，W.，Chen，E.，Hsu，N.，和J.Klensin，“中文域名的注册和管理建议”，RFC 4713，2006年10月。
[Unicode-UAX31] The Unicode Consortium, "Unicode Standard Annex #31: Unicode Identifier and Pattern Syntax, Revision 11", September 2009, <http://www.unicode.org/reports/tr31/tr31-11.html>.
[Unicode-UAX31]Unicode联盟，“Unicode标准附录31：Unicode标识符和模式语法，第11版”，2009年9月<http://www.unicode.org/reports/tr31/tr31-11.html>.
[Unicode-UTS39] The Unicode Consortium, "Unicode Technical Standard #39: Unicode Security Mechanisms, Revision 2", August 2006, <http://www.unicode.org/reports/tr39/tr39-2.html>.
[Unicode-UTS39]Unicode联盟，“Unicode技术标准#39:Unicode安全机制，第2版”，2006年8月<http://www.unicode.org/reports/tr39/tr39-2.html>.
Author's Address
作者地址
John C Klensin 1770 Massachusetts Ave, Ste 322 Cambridge, MA 02140 USA
美国马萨诸塞州剑桥322号马萨诸塞大道1770号约翰·C·克伦辛邮编：02140
Phone: +1 617 245 1457
EMail: john+ietf@jck.com
Phone: +1 617 245 1457
EMail: john+ietf@jck.com