[precis] names and usernames

[Peter Saint-Andre <[e-mail]>]

John Klensin has brought to my attention that it is currently impossible 
to represent some people's names in PRECIS usernames because some of the 
relevant Unicode code points are disallowed by the IdentifierClass 
defined in RFC 7564 (and thus by the UsernameCaseMapped and 
UsernameCasePreserved profiles defined in RFC 7613).

First, RFC 7564 disallows "default ignorable" code points in the 
IdentifierClass. However, as I understand it some of these code points 
are need to represent characters in names that might be desirable to 
people living within communities that use Indic script and eastern 
Arabic script (e.g., Persian and writing systems derived from Persian). 
In particular, the Unicode Standard specifies that ZWJ and ZWNJ are 
"default ignorable" and it seems that these code points are especially 
important in this context.

Second, apparently some Chinese family names are typically written 
(especially outside the People's Republic of China) using characters 
that the Unicode Consortium assigns to non-BMP code points, or assigns 
in the BMP but as compatibility decomposable characters (and thus 
disallowed by RFC 7564 in the IdentifierClass).

I'm not sure whether we can solve these problems (internationalization 
is messy and we've never tried to guarantee that any particular name or 
preferred string could be represented in PRECIS usernames), but input 
from people with a deeper understanding of these issues would be 
appreciated. I have attempted to reach out to relevant experts, and will 
report back to this list with any findings.

In the meantime, I plan to submit revised I-Ds addressing other issues 
with the PRECIS specifications sometime this evening.

Peter