ietf-nntp 9.4.9 PAT

[Andrew Gierth]

draft-ietf-nntpext-base-08.txt sez:

  9.4.9 PAT

            PAT header range|<message-id> [pat [pat...]]

            The PAT command is used to retrieve specific headers from
            specific articles, based on pattern matching on the contents
            of the header.
        [yadda]
            default. Successful responses start with a 221 response
            followed by article number, an US-ASCII space, and the header
            from that message in which the pattern matched the contents of
            the specified header line. A valid response includes an empty
            list (indicating that there were no matches). Once the output
            is complete, a period is sent on a line by itself. If the
            optional argument is a message-id and no such article exists,
            a 430 error response shall be returned. A 502 response shall
            be returned if the client only has permission to transfer
            articles.

It is becoming common for server implementations to refuse to perform
XPAT (and hence presumably PAT in future) on headers that are not part
of the overview or otherwise pre-indexed.

The above does not give any indication as to what error (if any) to
return in such a case.

-- 
Andrew.