Re: [idn] length restrictions on IDN label

[Soobok Lee <lsb@postel.co.kr>]

Adam M. Costello wrote:

>  
> IDNA created some brand new kinds of labels that had never existed
> before: non-ASCII textual labels.  They have never appeared in DNS,
> cannot appear in DNS, and will not be able to appear in DNS unless DNS
> is updated to support them (because the only text supported by today's
> DNS is ASCII).  These new non-ASCII textual labels are outside the
> universe of labels defined by RFC 1035, and therefore the RFC 1035
> length restriction does not apply to them (not directly, although it
> applies to their corresponding ASCII forms).
Okay.
non-ACE textual labels can be used and rendered in document format.

But, IDNA section 6.1 goes further than that
by allowing _protocols_ to use non-ACE labels  which are
not presentation forms nor textual labels, but protocol elements.
What if future ESMTP allows utf8 encodings in RCPT: headers ?

Would you comment on this section?

6.1 Entry and display in applications

(snip)

In protocols and document formats that define how to handle
specification or negotiation of charsets, labels can be encoded in any
charset allowed by the protocol or document format. If a protocol or
document format only allows one charset, the labels MUST be given in
that charset.

In any place where a protocol or document format allows transmission of
the characters in internationalized labels, internationalized labels
SHOULD be transmitted using whatever character encoding and escape
mechanism that the protocol or document format uses at that place.