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Re: questions about element declarations



At 07:31 PM 9/23/96 CDT, Michael Sperberg-McQueen wrote:
>* Should XML retain SGML's prohibition on multiple declarations for the
>same element (11.2.1)?

Yes. It should be an error. What would be the advantage of keeping them?
If you want to be able to redefine elements in the instance, this would
add some flexibility, but I wonder if it isn't flexibility that would
only lead to confusion.

If you allow them, then you'd want to discard any redefinition of the
element, otherwise you force the parser to go back and rebuild that whole
structure. I'd also ask that it be made optional so that I could turn it
off. I wouldn't want anyone to be able to redefine elements in the
instance.

>*  Should XML restrict the use of #PCDATA to content models of the form
>(#PCDATA), or of the form (#PCDATA | A | B | ...)*, as a way of avoiding
>the mixed-content trap (11.2.4) and/or of simplifying RE handling
>(7.6.1)?

This could be a non-issue depending on what the decision is on how we're
going to deal with RS/RE in general.

>* Should XML prohibit the use of inclusion and exclusion exceptions in
>element declarations? (11.2.4, 11.2.5)?

Inclusions can go away. Exclusions can be useful and it would be nice
if we could retain them.

>* Should XML prohibit content-model references to undeclared elements
>(11.2.4)?

It's really convenient to decompose element declarations in the DTD, but
I could live without it if it'll save a chunk of code for the parser writer.
However, it would make a typical customization scheme difficult wherein
some "local" elements are declared in the internal subset. If multiple
element declarations are disallowed, it could make it impossible. We don't
use this scheme, however, so I don't care.

>* Should XML forbid use of the '&' connector in content models
>(11.2.4.1)?

This is another one that I could live without if it will make a significant
savings to the parser writer. It'd force some rather gnarly looking
content models, but I'm much less concerned about inconvenience in the DTD
than I am in the instance.

>* Should XML allow nondeterministic content models (11.2.4.3)?

No.

bob


Robert Streich				streich@slb.com
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