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Date: Thu, 3 Jan 2013 10:09:32 +0000
From: Tony Finch <dot@dotat.at>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
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Subject: Re: [abnf-discuss] How to indent ABNF figures in draft?
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Paul Kyzivat <pkyzivat@alum.mit.edu> wrote:
>
> The ABNF syntax requires rules to start at the beginning of a line with no
> preceding whitespace.

Well, sort of. That's what the grammar says but there is an informal
permission to indent in RFC 5234 section 2.2:

   For visual ease, rule definitions are left aligned.  When a rule
   requires multiple lines, the continuation lines are indented.  The
   left alignment and indentation are relative to the first lines of the
   ABNF rules and need not match the left margin of the document.

This would ideally be part of the ABNF grammar.

Apart from comments, I don't think there is any need for ABNF to be
sensitive to newlines or indentation, though a parser would need two
tokens of lookahead to tell the difference between the end of a rule
(rulename defined-as) and a continued rule (rulename anything-else).

I suggest the following, which still requires rules to start on new lines
but removes sensitivity to horizontal white space.

         rulelist       =  1*( *c-wsp rule ) *c-wsp

         rule           =  rulename defined-as elements c-nl

         c-wsp          =  WSP / c-nl

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