Subject: #540 clarify ABNF layering

From: Julian Reschke <[email-masked]>
Date: Sat, 28 Dec 2013 15:36:02 +0100

<http://trac.tools.ietf.org/wg/httpbis/trac/ticket/540>:

Pete Resnick wrote:

> Throughout the document (and the other documents in the series): I now understand that you intend a two stage parse for header fields and have that represented in the ABNF as a separate overall message syntax and a header field value syntax. That's fine, but I would ask that you make this clearer somewhere in section 3 of the p1 document. You talk about the parsing, but I think it is well worth describing that there are two levels of ABNF, and that the ABNF rule name corresponds to the header field name. It is fine to do it this way, but it's not the way that ABNF has been used in the past, so best to make it crystal clear.

Maybe add to the end of Part 1, Section 3.2:

"The field-name token labels the corresponding field-value as having the 
semantics defined by that header field. For example, the Date header 
field is defined in Section 7.1.1.2 of [Part2] as containing the 
origination timestamp for the message in which it appears.

Extraction of field-name/field-value pairs from a message is generic and 
thus independent of the actual field name. Consequently, the ABNF 
specified for each header field only defines the syntax of the 
field-value (not the whole header-field, as it was the case in previous 
revisions of this specification)".

Feedback appreciated, Julian

---

From: Mark Nottingham <[email-masked]>
Date: Wed, 1 Jan 2014 14:50:53 +1100

Works for me.

On 29 Dec 2013, at 1:36 am, Julian Reschke <[email-masked]> wrote:

> "The field-name token labels the corresponding field-value as having the semantics defined by that header field. For example, the Date header field is defined in Section 7.1.1.2 of [Part2] as containing the origination timestamp for the message in which it appears.
> 
> Extraction of field-name/field-value pairs from a message is generic and thus independent of the actual field name. Consequently, the ABNF specified for each header field only defines the syntax of the field-value (not the whole header-field, as it was the case in previous revisions of this specification)".
> 

--
Mark Nottingham   http://www.mnot.net/