Re: [ietf-dkim] Re: Use of LWSP in ABNF -- consensus call

Tony Finch <dot@dotat.at> Thu, 17 May 2007 23:38 UTC

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Date: Fri, 18 May 2007 00:38:15 +0100
From: Tony Finch <dot@dotat.at>
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To: John C Klensin <john-ietf@jck.com>
Subject: Re: [ietf-dkim] Re: Use of LWSP in ABNF -- consensus call
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On Thu, 17 May 2007, John C Klensin wrote:
>
> 	(1) Other specifications that use the term "LWSP" to
> 	refer to something different from what is unambiguously
> 	defined in the ABNF spec.
>
> [This] group is, IMO, just broken.

I agree with your sentiment but sadly there's a lot of old stuff that's
broken by this criterion. RFC 733 defined <LWSP-char> to mean what RFC
2234 calls <WSP>, and <linear-white-space> to mean what is now <LSWP>.
Fortunately these old definitions have fallen out of use. There's also
HTTP and SIP which call the problematic production <LWS> instead of
<LWSP>. MEGACO uses ABNF with its own terminal definitions instead
of referring to ABNF appendix B. CGI uses its own ABNF variant.

It would be nice if the progression of ABNF to a full standard reduces
this Babel. This implies that (a) ABNF should be used to describe syntax
in preference to any other BNF-alike, to avoid anomalies like CGI; (b)
specifications should not define a production with the same name as one in
appendix B but with a different expansion, to avoid anomalies like MEGACO;
(c) specifications should not define a production with the same expansion
as one in appendix B but with a different name, to avoid anomalies like
HTTP and SIP; (d) any production like LWSP should be discouraged because
of problems with lossage related to trailing whitespace.

Tony.
-- 
f.a.n.finch  <dot@dotat.at>  http://dotat.at/
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