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Re: Optional Extensions

From: Mark Baker <distobj@acm.org>
Date: Wed, 28 Jan 2004 15:48:02 -0500
To: www-ws-desc@w3.org
Message-ID: <20040128154802.R2245@www.markbaker.ca>

On Wed, Jan 28, 2004 at 11:58:27AM -0800, Prasad Yendluri wrote:
> Good point. What if the definition of the optional extension is "faulty" 
> :).
> Well I guess we would have come full circle on this if we do end up with 
> optional extensions MAY be ignored.

What's important here is that an expectation be created amoungst
would-be extenders that their extensions won't break existing software.
"MUST" definitely does that. "SHOULD" does too, though less
emphatically.  "MAY" does not; you might have noticed that RFC 2119 does
not define "MAY NOT", as it's semantically equivalent to "MAY".

FWIW, HTTP uses SHOULD, and that seems to suffice;

   The extension-header mechanism allows additional entity-header fields
   to be defined without changing the protocol, but these fields cannot
   be assumed to be recognizable by the recipient. Unrecognized header
   fields SHOULD be ignored by the recipient and MUST be forwarded by
   transparent proxies.
    -- http://www.ietf.org/rfc/rfc2616, sec 7.1

So, does "SHOULD ignore" work for everyone?

Mark.
-- 
Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Received on Wednesday, 28 January 2004 15:48:29 GMT

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