New Last Call: 'Tags for Identifying Languages' to BCP

Brian Rosen br at
Sat Dec 18 20:56:55 CET 2004

I don't have any comment on the issue of language tags, but speaking as a
reasonably avid ABNF hacker, I agree with Sam, and would not want to
establish a convention that ABNF in IETF RFCs is expected to be precise.
One MUST read the text to understand what the limits of the syntax are.
This is especially true with repetitions.  It's usually tortuous to write
ABNF that limits repetitions or string lengths.  It's possible, but the
result is very hard to understand.


> -----Original Message-----
> From: ietf-bounces at [mailto:ietf-bounces at] On Behalf Of
> Sam Hartman
> Sent: Saturday, December 18, 2004 1:55 PM
> To: ietf-languages at
> Cc: ietf at
> Subject: Re: New Last Call: 'Tags for Identifying Languages' to BCP
> >>>>> "Bruce" == Bruce Lilly <blilly at> writes:
>     Bruce> If there really are only 24 items of less than 11 octets
>     Bruce> each, a trivial solution is to simply list them (with the
>     Bruce> usual ABNF syntax) as literal strings.  That should take no
>     Bruce> more than a half-dozen lines.
> Perhaps.  I actually find a lot of ABNF specs are not as clear as they
> could be to humans because they are trying to describe the valid
> inputs as strictly as possible.  In many cases I think the spec would
> be more clear if the ABNF were relaxed and other constraints were
> expressed at appropriate levels.
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