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Re: Request to relax PCDATA content model restriction

From: Norbert H. MIKULA <e_nmiku@utila.ifi.uni-klu.ac.at>
Date: Thu, 24 Apr 1997 17:46:37 +0200
Message-ID: <335F805C.1FD2@utila.ifi.uni-klu.ac.at>
To: "Eve L. Maler" <elm@arbortext.com>, w3c-sgml-wg@w3.org
Eve L. Maler wrote:
> 
> I've been corresponding with Terry Allen, who's doing an XMLish version of
> DocBook.  DocBook has a lot of content models like the following:
> 
>   ((%xxx.char.mix;)*)
> 
> where %xxx.char.mix; resolves to (#PCDATA|a|b|c...).  The current XML Lang
> spec doesn't allow for this; production 45 is very specific about how many
> pairs of parens can appear, rather than going for the generalized model
> group solution of productions 40-44.
> 
> Of course, the outermost parens aren't really necessary; you can achieve
> the desired effect with (%xxx.char.mix;)* instead of ((%xxx.char.mix;)*).
> But where content models are heavily parameterized and you can't easily see
> what kind of model you've got, this makes the DTD writer split hairs.
> 
> It should always be safe to throw another couple of paren pairs around a
> model, and currently in XML you can't do this.  Can we consider loosening
> this restriction?

I like the way it is handled now. However, I would be interested
in the way you would describe Production 45 in EBNF then. You are not
very specific about the alternative way you suggest.

I can see your point, from the perspective of a DTD designer. However,
we should try to keep things as simple as possible. (Maybe) XML
will require a slightly different approach to DTD design anyway.

-- 
Best regards,
Norbert H. Mikula

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Received on Thursday, 24 April 1997 11:45:25 EDT

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