Internet DRAFT - draft-msporny-d-langtag-ext
draft-msporny-d-langtag-ext
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.
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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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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
by key. The order of subtags within a keyword is significant; the
meaning of this extension is altered if those subtags are rearranged.
Thus, the canonical form of the extension never reorders the subtags
within a keyword.
2.2. Registration Form
Per RFC 5646, Section 3.7 [RFC5646]:
%%
Identifier: d
Description: Text Direction
Comments: Subtags for the identification of language direction. Used to
influence input mechanisms and graphical rendering.
Added: 2019-05-25
RFC: [TBD]
Authority: Manu Sporny
Contact_Email: msporny@digitalbazaar.com
Mailing_List: public-credentials@w3.org
URL: https://www.w3.org/2017/vc/WG/
%%
3. Acknowledgements
Thanks to Dan Burnett, Charles "chaals" Nevile, Dave Longley, Ivan
Herman, Rob Sanderson, Richard Ishida, Addison Philips, Benjamin
Young, Ivan Herman, Pierre-Antoine Champin, and Eric Prud'hommeaux
for the discussion that led to this specification.
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4. IANA Considerations
This document will require IANA to insert the record in Section 2.2
into the Language Extensions Registry, according to Section 3.7.
Extensions and the Extensions Registry of "Tags for Identifying
Languages" in [RFC5646].
This document does not require IANA to create or maintain a new
registry or otherwise impact IANA.
5. Security Considerations
The security considerations for this extension are the same as those
for [RFC5646]. See RFC 5646, Section 6, Security Considerations
[RFC5646].
6. Normative References
[RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[US-ASCII]
International Organization for Standardization, "ISO/IEC
646:1991, Information technology -- ISO 7-bit coded
character set for information interchange.", 1991.
Author's Address
Manu Sporny
Digital Bazaar
Email: msporny@digitalbazaar.com
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