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Date: Thu, 03 Jan 2013 11:06:50 -0500
From: Paul Kyzivat <pkyzivat@alum.mit.edu>
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To: Tony Finch <dot@dotat.at>
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Subject: Re: [abnf-discuss] How to indent ABNF figures in draft?
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On 1/3/13 5:09 AM, Tony Finch wrote:
> 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.

I guess it is a matter of how you read this.
It doesn't *look* normative. I took it to be describing a display 
convention for the document itself rather than an alteration to the 
syntax rules.

> This would ideally be part of the ABNF grammar.

It isn't possible to express *that* syntax rule in ABNF.

> 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).

Yes, that is a possible direction.

> 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

Maybe. I like this better than allowing multiple rules per line with no 
explicit separators.

	Thanks,
	Paul

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