Mapping Characters for Classes of the Preparation, Enforcement, and Comparison of Internationalized Strings (PRECIS)
RFC 7790

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Internet Engineering Task Force (IETF)                         Y. Yoneya
Request for Comments: 7790                                          JPRS
Category: Informational                                        T. Nemoto
ISSN: 2070-1721                                          Keio University
                                                           February 2016

  Mapping Characters for Classes of the Preparation, Enforcement, and
            Comparison of Internationalized Strings (PRECIS)

Abstract

   The framework for the preparation, enforcement, and comparison of
   internationalized strings (PRECIS) defines several classes of strings
   for use in application protocols.  Because many protocols perform
   case-sensitive or case-insensitive string comparison, it is necessary
   to define methods for case mapping.  In addition, both the
   Internationalized Domain Names in Applications (IDNA) and the PRECIS
   problem statement describe mappings for internationalized strings
   that are not limited to case, but include width mapping and mapping
   of delimiters and other special characters that can be taken into
   consideration.  This document provides guidelines for designers of
   PRECIS profiles and describes several mappings that can be applied
   between receiving user input and passing permitted code points to
   internationalized protocols.  In particular, this document describes
   both locale-dependent and context-depending case mappings as well as
   additional mappings for delimiters and special characters.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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.

   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/rfc7790.

Yoneya & Nemoto               Informational                     [Page 1]
RFC 7790                     PRECIS Mapping                February 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Protocol-Dependent Mappings . . . . . . . . . . . . . . . . .   3
     2.1.  Delimiter Mapping . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Special Mapping . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  Local Case Mapping  . . . . . . . . . . . . . . . . . . .   4
   3.  Order of Operations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  Mapping Type List  . . . . . . . . . . . . . . . . .   8
     A.1.  Mapping Type List for Each Protocol . . . . . . . . . . .   8
   Appendix B.  Why Local Case Mapping Is an Alternative to Case
                Mapping in the PRECIS Framework  . . . . . . . . . .   8
   Appendix C.  Limitations of Local Case Mapping  . . . . . . . . .   9
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   In many cases, user input of internationalized strings is generated
   through the use of an input method editor ("IME") or through copy-
   and-paste from free text.  Users generally do not care about the case
   and/or width of input characters because they consider those
   characters to be functionally equivalent or visually identical.
   Furthermore, users rarely switch the IME state to input special
   characters such as protocol elements.

Yoneya & Nemoto               Informational                     [Page 2]
RFC 7790                     PRECIS Mapping                February 2016

   For Internationalized Domain Names (IDNs), the IDNA Mapping