Doug Ewell doug at ewellic.org
Fri Feb 22 17:09:37 CET 2013

Draft-gellens-negotiating-human-language-01, "Negotiating Human Language
Using SDP", says this about the source of values for the SDP 'lang'

> The "lang" attribute value must be a single [RFC3066] language tag
> in US-ASCII [RFC3066].

Although this wording is quoted from RFC 4566, the subsequent section
proposing a new 'humintlang' attribute uses the same wording.

Any new format or protocol that employs language tags should apply BCP
47 (RFC 5646), not RFC 3066, which was obsoleted in 2006. BCP 47 allows
the use of more than 7300 additional language subtags derived from ISO
639-3, as well as script subtags based on ISO 15924 and variant subtags,
none of which are permitted in a generative manner by RFC 3066.

The draft says, "The attribute value should be a language tag from the
IANA registry [IANA-lang-tags]", referencing
www.iana.org/assignments/language-subtag-registry, but RFC 3066 does not
use this registry; it references the core ISO standards directly, which
reduces stability, and it uses its own IANA registry (also obsolete)
only for a few dozen predefined variant tags, many of which are
deprecated in BCP 47. 

RFC 4647, also part of BCP 47, provides guidelines for matching language
tags, and may benefit the SDP negotiation process described in the

Doug Ewell | Thornton, CO, USA
http://ewellic.org | @DougEwell ­

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