RFC 7940: Representing Label Generation Rulesets Using XML | RFC Editor

Skip to content Primary navigationThe RFC SeriesFor AuthorsAbout UsHomeRFC 7940 View as: Plain Text, Compact HTML Info RFC 7940: Representing Label Generation Rulesets Using XMLXMLIDNAugust 2016. K. Davies, A. FreytagProposed StandardSubscribe4 subscribed Add to Set Added to 2 Sets Read aloud Internet Engineering Task Force (IETF) K. Davies Request for Comments: 7940 ICANN Category: Standards Track A. Freytag ISSN: 2070-1721 ASMUS, Inc. August 2016 Representing Label Generation Rulesets Using XML Abstract This document describes a method of representing rules for validating identifier labels and alternate representations of those labels using Extensible Markup Language (XML). These policies, known as "Label Generation Rulesets" (LGRs), are used for the implementation of Internationalized Domain Names (IDNs), for example. The rulesets are used to implement and share that aspect of policy defining which labels and Unicode code points are permitted for registrations, which alternative code points are considered variants, and what actions may be performed on labels containing those variants. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. 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/rfc7940. Davies & Freytag Standards Track [Page 1] RFC 7940 Label Generation Rulesets in XML August 2016 Copyright Notice Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. 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. Table of Contents 1. Introduction ....................................................4 2. Design Goals ....................................................5 3. Normative Language ..............................................6 4. LGR Format ......................................................6 4.1. Namespace ..................................................7 4.2. Basic Structure ............................................7 4.3. Metadata ...................................................8 4.3.1. The "version" Element ...............................8 4.3.2. The "date" Element ..................................9 4.3.3. The "language" Element ..............................9 4.3.4. The "scope" Element ................................10 4.3.5. The "description" Element ..........................10 4.3.6. The "validity-start" and "validity-end" Elements ...11 4.3.7. The "unicode-version" Element ......................11 4.3.8. The "references" Element ...........................12 5. Code Points and Variants .......................................13 5.1. Sequences .................................................14 5.2. Conditional Contexts ......................................15 5.3. Variants ..................................................16 5.3.1. Basic Variants .....................................16 5.3.2. The "type" Attribute ...............................17 5.3.3. Null Variants ......................................18 5.3.4. Variants with Reflexive Mapping ....................19 5.3.5. Conditional Variants ...............................20 5.4. Annotations ...............................................22 5.4.1. The "ref" Attribute ................................22 5.4.2. The "comment" Attribute ............................23 5.5. Code Point Tagging ........................................23 Davies & Freytag Standards Track [Page 2] RFC 7940 Label Generation Rulesets in XML August 2016 6. Whole Label and Context Evaluation .............................23 6.1. Basic Concepts ............................................23 6.2. Character Classes .........................................25 6.2.1. Declaring and Invoking Named Classes ...............25 6.2.2. Tag-Based Classes ..................................26 6.2.3. Unicode Property-Based Classes .....................26 6.2.4. Explicitly Declared Classes ........................28 6.2.5. Combined Classes ...................................29 6.3. Whole Label and Context Rules .............................30 6.3.1. The "rule" Element .................................31 6.3.2. The Match Operators ................................32 6.3.3. The "count" Attribute ..............................33 6.3.4. The "name" and "by-ref" Attributes .................34 6.3.5. The "choice" Element ...............................34 6.3.6. Literal Code Point Sequences .......................35 6.3.7. The "any" Element ..................................35 6.3.8. The "start" and "end" Elements .....................35 6.3.9. Example Context Rule from IDNA Specification .......36 6.4. Parameterized Context or When Rules .......................37 6.4.1. The "anchor" Element ...............................37 6.4.2. The "look-behind" and "look-ahead" Elements ........38 6.4.3. Omitting the "anchor" Element ......................40 7. The "action" Element ...........................................40 7.1. The "match" and "not-match" Attributes ....................41 7.2. Actions with Variant Type Triggers ........................41 7.2.1. The "any-variant", "all-variants", and "only-variants" Attrib