Representing Label Generation Rulesets Using XML
RFC 7940

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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