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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 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 Provisions Relating to IETF Documents (https://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. Sporny Expires November 26, 2019 [Page 1] Internet-Draft BCP 47 Text Direction May 2019 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]. Sporny Expires November 26, 2019 [Page 2] Internet-Draft BCP 47 Text Direction May 2019 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. Sporny Expires November 26, 2019 [Page 3] Internet-Draft BCP 47 Text Direction May 2019 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, . [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 Sporny Expires November 26, 2019 [Page 4]