BCP 47 Extension D
draft-msporny-d-langtag-ext-00

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Internet Engineering Task Force                                M. Sporny
Internet-Draft                                            Digital Bazaar
Intended status: Informational                              May 25, 2019
Expires: November 26, 2019

                           BCP 47 Extension D
                     draft-msporny-d-langtag-ext-00

Abstract

   This document specifies an Extension to BCP 47 which provides subtags
   that specify language direction.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on November 26, 2019.

Copyright Notice

   Copyright (c) 2019 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
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   (https://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  RFC5646 Required Information  . . . . . . . . . . . . . . . .   2
     2.1.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .   2
       2.1.1.  Canonicalization  . . . . . . . . . . . . . . . . . .   3
     2.2.  Registration Form . . . . . . . . . . . . . . . . . . . .   3
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   [RFC5646] permits the definition and registration of language tag
   extensions "that contain a language component and are compatible with
   applications that understand language tags".  This document defines
   an extension for identifying text direction using language tags.  The
   "singleton" identifier for this extension is 'd'.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

2.  RFC5646 Required Information

   Language tags, as defined by [RFC5646], are useful for identifying
   the language of content.  Some operating environments also use the
   language tag to determine text direction, which can be problematic.
   This extension provides a mechanism for explicitly stating the
   direction of a specific language-tagged string.

2.1.  Summary

   The subtags available for use in the 'd' extension consist of the
   values 'ltr', 'rtl', and 'auto' for expressing text direction that is
   "left-to-right", "right-to-left", and "automatically detected",
   respectively.

   For example, the language tag "ar-d-rtl" consists of:

   o  The base language tag "ar" (Arabic), exactly as defined by
      [RFC5646].

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   o  The singleton 'd', identifying this extension.

   o  The attribute 'rtl', which specifies a direction of "right to
      left".

   Only the first occurrence of an attribute or key conveys meaning in a
   language tag.  When interpreting tags containing the direction
   extension, duplicate attributes or keywords are ignored in the
   following way: ignore any attribute that has already appeared in the
   tag and ignore any keyword whose key has already occurred in the tag.

2.1.1.  Canonicalization

   As required by [RFC5646], the use of uppercase or lowercase letters
   is not significant in the subtags used in this extension.  The
   canonical form for all subtags in the extension is lowercase.  The
   canonical order of attributes is in [US-ASCII] order (that is,
   numbers before letters, with letters sorted as lowercase US-ASCII
   code points).  The canonical order of keywords is in [US-ASCII] order
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