RRP and language tags

[Removing unicode <at> unicode.org and adding dam <at> icann.org]

Yesterday, it seemed like some people agreed with me that, in the 
general case, the language tag being passed in the RRP protocol is not 
just naming a character table to filter against, but, more generally, a 
set of rules that the registry applies to determine registerability.

Ignoring for now whether we can decide that there is consensus on this 
issue, I'd like to explore the issues some more, and ask a few 
questions, if that's OK.

First, the language tag is just a name, so in some sense it does not 
really matter *what* it is naming, whether that be a human language, a 
registry's table of characters, or a registry's set of rules. But if we 
can show that ISO 639 is not an adequate namespace, then we may wish to 
consider a new namespace.

One reason that 639 might not be adequate is that some languages are 
used in more than one part of the world, and that usage may differ 
enough from one community to another that we want to assign two separate 
codes instead of a single 639 code. A very common way to go about this 
is to simply add a country code (ISO 3166).

However, currently it seems like the trend is to have a number of sets 
of rules, one at each NIC. The .jp registry has a table and some rules, 
the .de registry has a table, and so on. Some organizations appear to be 
working together to unify their methods. China and Taiwan come to mind. 
This trend might lead one to think that the RRP tag should not be a 
language, but simply the name of a NIC or TLD or pair of TLDs.

But this might be too restrictive. What if some organization or 
individual comes up with a set of rules that is desirable for a number 
of reasons, such as the inclusion of a large number of characters? Some 
registries may wish to allow registrars (and by extension, registrants) 
to specify the use of such a set of rules.

This would argue for maximum flexibility in the RRP tag namespace. I.e. 
it should not be limited to 639 or to 639+3166 or to ccTLD name. It 
could just be a separate namespace, possibly with an IANA registry, 
similar to the numerous other namespaces registered there. Charsets come 
to mind, but there are many others. Such a new namespace would even 
allow for private agreements, which usually have names that start with 
"x-" in other IANA namespaces.

Any thoughts on these ideas?

And now for the questions: Where is this RRP spec? Is it an RFC? Which 
RRP document specifies the language tag we have been talking about?

Do all of the registries use RRP? If not, what do they use? And do they 
have language tags?

Thanks,

Erik