Unstructured: DSD syntax.

   I love the idea. It's simple to implement, simpler to explain: "Here are
the new tags that XML gives you for declaring new tags in your documents."

   The one thing that should be changed is the syntax for content models.
Content models are fine in the current DTD notation. An simple expression
language isn't hard to parse, so that should not be an issue, even though
it does add 3 productions or so. Maybe a few more than that, if we don't
fix SMGL's weird rules about where parentheses can go. Worse, the element
syntax for content models enhances the impression that model groups are
syntactically meaningful, providing a future obstacle to full regexp
content models. I think this would also solve one of the main sources of
bloat in the DSD examples.

   I'd also like to have a way to put comments in a DSD. Perhaps a
<comment> element that would be legal anywhere in a DSD following a special
declaration of its content model. Maybe we could do some hack like
<#comment> containing other #tags that would only be usable in the DSD.
Then I could really make my DSDs into documents.

On meta-meta-languages:

  As far as the syntax of DSDs confusing user by blurring the distinction
between markup and meta-data: I don't believe it. DSD contents can be
simply described as tag-extending tags.

    The meta-language distinction in SGML is way too esoteric and is
blurred most of the time anyway. Here's my (linguist/computer
science/logic) take on SGML as a metalanguage. The confusion comes about
because 8879 defines both a metalanguage (the syntax and semantics of DTDs)
as well as the meta-syntax for a family of languages, each describable by a
DTD, option specifications, and arbitrary numerical limits. And these
tagging languages themselves are correctly  used to describe meta-data
about the linguistic content of the documents they are applied to. We have
at least 3 meta-levels here; we're unlikely to ever have an accurate
sound-bite description of what SGML really is from this perspective.

David Durand              dgd@cs.bu.edu  \  david@dynamicDiagrams.com
Boston University Computer Science        \  Sr. Analyst
http://www.cs.bu.edu/students/grads/dgd/   \  Dynamic Diagrams
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