Multiple preferred values [was: Add retired tag "eml" to the IANAregistry]

[Randy Presuhn]

Hi -

> From: "Michael(tm) Smith" <mike at w3.org>
> To: "Phillips, Addison" <addison at amazon.com>
> Cc: <ietf-languages at alvestrand.no>
> Sent: Sunday, December 13, 2009 11:10 PM
> Subject: Multiple preferred values [was: Add retired tag "eml" to the IANAregistry]
>
> "Phillips, Addison" <addison at amazon.com>, 2009-12-11 00:45 -0500:
> 
> [...]
> > 2. I don't believe that your requested Preferred-Value is valid.
> > Each Preferred-Value must contain exactly one subtag and there
> > can be only one P-V field per record.
> 
> If it's anticipated that there's any possibility in the future of
> tags being split, it would seem like there might be a need to have
> a means to specify multiple preferred values.

BCP 47 doesn't allow multiple Preferred-Value fields, and, more
importantly, it doesn't allow splitting a tag.  The impact of an ISO
decision to split would be the creation of new subtags, most likely
as variants, to identify the distinction.  The impact of this approach
on legacy applications and data is little different from a decision to
broaden.  In both cases, the result is that legacy data's tagging may
become less precise (but no less accurate) than was the
intent of the original tagger.

As currently formulated, a Preferred-Value can be acted
on blindly and automatically, and could be used to automate
the re-tagging of legacy data if one really wanted to do such
a thing.  If there could be multiple ones, this would no longer
be true.

Randy