Re: [apps-discuss] draft-yevstifeyev-abnf-separated-lists-01.txt

[Julian Reschke <[e-mail]>]

On 06.12.2010 21:16, John C Klensin wrote:
> ...
> IMO, that case has not been made at all convincingly yet.  The
> sorts of examples that Barry and Tony suggest would be a useful
> step in the process of convincing people, but I suggest that,
> unless it can be shown that this construction actually
> simplifies a large number of practical cases, every error we
> find in the ABNF when documents that use the metalanguage are
> examine is an argument against more operators and complexity.
> ...

Right.

We spent a considerable amount of time in 2008 and 2009 on HTTPbis ABNF 
work, and we ended up *keeping* the # syntax for the actual spec text, 
but added a normative mapping to RFC 5234 ABNF, and also have 
auto-generated appendices with the expanded notation.

See

 
<http://greenbytes.de/tech/webdav/draft-ietf-httpbis-p1-messaging-latest.html#notation.abnf>

and

 
<http://greenbytes.de/tech/webdav/draft-ietf-httpbis-p1-messaging-latest.html#collected.abnf>

If we *were* adding features to RFC 5234, the one thing I'm missing most 
is a shorthand notation for defining a set of characters as a difference 
from another set, such as

   myoctdigits = DIGIT - ( "8" / "0" )

Without this feature, many people use prose production instead ("<VCHAR 
except ...>"), or create proper ABNF which then is hard to follow.

Best regards, Julian