Re: [idn] naming syntax rules

[John C Klensin <klensin@jck.com>]

--On Saturday, 08 December, 2001 11:12 +0100 Dan Oscarsson
<Dan.Oscarsson@trab.se> wrote:

> While this is good, to make DNS really work the foundamental
> rules should be the same for all labels. Just like it has been
> so far.
>... 
> For all labels in DNS (including host name and mailbox):
> - They must be case-insensitivly matched.
> - They must retain original form (not converted to lower case)
>   in DNS.

I agree, but note that we haven't been able to really determine
what "case-insensitive" means for a number of non-ASCII scripts.

> Having the above set in place, applications can apply additional
> rules and they can change over time without the basic DNS
> workings having to be changed.

Very desirable, if feasible.

> Mailbox labels:
> - In DNS they are not case-sensitive. Some mail systems are said
>   to have them case-sensitive. Are there still some such ancient
>   systems left?

I assume that, by "mailbox label" you are talking about the label
on an MX record (or an A RR that will be promoted to one).  From
the standpoint of a mail system, this is the mailbox domain, with
the mailbox name consisting of a local-part and that mailbox
domain.

Given that definition, I'm not aware of any surviving mail
systems that still give a case-sensitive interpretation to the
mailbox domain.  More important, that behavior has never been
valid (even before the DNS was deployed).    On the other hand,
if you really mean "mailbox name", interpretation of the
local-part is up to the receiving server (the server that hosts
the mailbox or mail store or non-SMTP interface to it).
Case-sensitive interpretation is not recommended, but has always
been, and is still, valid.

> What characters should be allowed in a label?
> Above I have defined it to be printable characters.
> Looking at how names are used, I would like to restrict
> it further. A name is often used as part of a text (for example
> in a manual or a web page). You then do not want the name
> to affect the formatting of the text. So you cannot allow
> anything in a name that affects direction, width, size,
> boldness, etc. So things like double width characters should
> not be allowed. This should probably be included in the
> definition of
> what is normalised text. Things like upper/lower case do not
> change the formatting of the text and can be used to enhance
> meaning or readability, and should be retained.

We agree.  An extension of this argument leads to excluding
drawing, symbols, space and non-spacing break, and punctuation
characters too (assuming they can be identified).  But my sense
is that we are in the minority of the WG in that preference.

    john