Re: Use of LWSP in ABNF -- consensus call

Philip Guenther <> Thu, 17 May 2007 15:58 UTC

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Date: Mon, 14 May 2007 19:59:29 -0600
From: Philip Guenther <>
To: Lisa Dusseault <>
Subject: Re: Use of LWSP in ABNF -- consensus call
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On Mon, 14 May 2007, Lisa Dusseault wrote:
> The IESG reviewed 
> <> for 
> publication as Internet Standard and would like to know if there is consensus 
> to recommend against the use of LWSP in future specifications, as it has 
> caused problems recently in DKIM and could cause problems in other places.

LWSP was one of the factors in the SASL WG's abandoning of the DIGEST-MD5 
revision.  To be precise, the complexity inherent in the 822-style n#rule 
syntax (the emulation of which in modern ABNF uses LWSP) was found to be a 
source of implementation errors and interoperability issues.  Part of the 
discussion can be seen at:

While I don't think removing LWSP from the ABNF RFC is good idea, adding a 
comment to its definition in section B.1 that warns protocol designers to 
consider carefully whether they really need or want "LWSP" instead of 
"*WSP" does seem appropriate.  Calling out that LWSP permits lines 
containing just whitespace may help drive home the issue.

Philip Guenther
Sendmail, Inc