Variant Rules
draft-freytag-lager-variant-rules-04

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Last updated 2017-03-14 (latest revision 2017-03-13)
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Network Working Group                                         A. Freytag
Internet-Draft                                            March 13, 2017
Intended status: Informational
Expires: September 14, 2017

                             Variant Rules
                  draft-freytag-lager-variant-rules-04

Abstract

   Rules for validating identifier labels and alternate representations
   of those labels (variants) are known as "Label Generation Rulesets"
   (LGRs); they are used for the implementation of identifier systems
   such as Internationalized Domain Names (IDNs).  This document
   describes ways of designing Label Generation Rulesets (LGRs) that
   support variant labels.  In designing LGRs, it is important to ensure
   that the label generation rules are consistent and well-behaved in
   the presence of variants.  The design decisions can then be expressed
   using the an XML representation of LGRs that is defined in RFC7940.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 14, 2017.

Copyright Notice

   Copyright (c) 2017 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

Freytag                Expires September 14, 2017               [Page 1]
Internet-Draft Using Variants in Label Generation Rulesets    March 2017

   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Variant Relationships . . . . . . . . . . . . . . . . . . . .   4
   3.  Symmetry and Transitivity . . . . . . . . . . . . . . . . . .   4
   4.  A Word on Notation  . . . . . . . . . . . . . . . . . . . . .   5
   5.  Variant Mappings  . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Variant Labels  . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Variant Types and Label Dispositions  . . . . . . . . . . . .   6
   8.  Allocatable Variants  . . . . . . . . . . . . . . . . . . . .   7
   9.  Blocked Variants  . . . . . . . . . . . . . . . . . . . . . .   8
   10. Pure Variant Labels . . . . . . . . . . . . . . . . . . . . .   9
   11. Reflexive Variants  . . . . . . . . . . . . . . . . . . . . .  10
   12. Limiting Allocatable Variants by Subtyping  . . . . . . . . .  10
   13. Allowing Mixed Originals  . . . . . . . . . . . . . . . . . .  13
   14. Handling Out-of-Repertoire Variants . . . . . . . . . . . . .  14
   15. Conditional Variants  . . . . . . . . . . . . . . . . . . . .  15
   16. Making Conditional Variants Well-Behaved  . . . . . . . . . .  16
   17. Variants for Sequences  . . . . . . . . . . . . . . . . . . .  18
   18. Corresponding XML Notation  . . . . . . . . . . . . . . . . .  19
   19. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  21
   20. Security Considerations . . . . . . . . . . . . . . . . . . .  21
   21. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     21.1.  Normative References . . . . . . . . . . . . . . . . . .  22
     21.2.  Informative References . . . . . . . . . . . . . . . . .  22
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  22
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  22
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   Label Generation Rulesets (LGRs) that define the set of permissible
   labels, may be applied to a variety of identifier systems, although
   to date, the most common use is to define policies for implementing
   Internationalized Domain Names (IDNs) for some zone of the Domain
   Name System (DNS).  Without restricting any of the more general
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