Re: [ietf-822] [abnf-discuss] Wherefore no HTAB in literal text strings in ABNF

Paul Overell <> Mon, 15 August 2016 09:02 UTC

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To: Sean Leonard <>, ABNF-Discuss <>,
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From: Paul Overell <>
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Date: Mon, 15 Aug 2016 10:02:20 +0100
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Subject: Re: [ietf-822] [abnf-discuss] Wherefore no HTAB in literal text strings in ABNF
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On 15/08/16 02:34, Sean Leonard wrote:
> Hello Knowledgeable ABNF Folks:
> I have been working with RFC 5234 lately. What is the rationale (or what are the rationales) for including SP %d32 but excluding HTAB %d9 in char-val, aka the literal text string? I am sure that this decision was not an oversight.
> It may be appreciated that the comment production is defined as WSP, which includes HTAB.

   char-val       =  DQUOTE *(%x20-21 / %x23-7E) DQUOTE
                                ; quoted string of SP and VCHAR
                                ;  without DQUOTE

So that the contents of a string literal are visible and unambiguous to
a human reader - spaces and tabs look alike.  For comments is doesn't
matter if the white space comprises of spaces or tabs, it doesn't change
the meaning of a comment.  But for strings it's important for a human
reader to know exactly what's in them.


Paul Overell