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Standardized tag (was: draft-klensin-rfc2821bis-10: ABNF discuss)

2008-07-01 17:25:26

At 03:02 30-06-2008, Magnus Westerlund wrote:
As some may have seen I held a discuss in two parts. The second part was unfortunately not discussed until last week at all with me. I would like to get your input into this question.

My discuss was started due to there was a rule which wasn't a rule, i.e. it didn't contain any elements. A clear syntax violation in ABNF. The rule in the issue was "Standardized-tag", this can be seen in version 10 of the draft in section 4.1.3.

The question was raised by Frank in 2007.

Quoting the section from RFC 2821:

   "For IPv6 and other forms of addressing that might eventually be
   standardized, the form consists of a standardized "tag" that
   identifies the address syntax, a colon, and the address itself, in a
   format specified as part of the IPv6 standards [17]."

That might have to be changed as well.

Is there a any problem with defining a rule for what characters is allowed in future tag for identifying literal address formats that is large enough to motivate living with the interoperability issue?

A point raised during the discussion was whether something is valid because it is permitted by the syntax. Some future document might have a case where IPv6 addresses with a scope identifier are covered in SMTP. That's where the standardized tag comes in. It can also apply to other forms of addressing.

One might have to go back all the way to 821 to fully understand the rationale of what's in this draft. And even then, it's not that obvious unless you talk to the people who actually wrote the text.