XML & SGML

[Paul Prescod]

Conleth O'Connell wrote:
> 
> The XML instance might look like:
> 
> <!DOCTYPE foo SYSTEM "http://mycom.com/f.dtd" [
> <!ENTITY % bar "baz | car | xyzzy">
> ]>
> 
> <foo><xyzzy/></foo>

Note that this sort of trickery is poorly supported by SGML editors. They
like to think of a DTD as a single immutable thing that spans documents
(as users do). But technically, DTDs are really just properties of
documents, and documents can fiddle with them as you demonstrate above. I
think that I would advise against depending on this sort of fiddling until
we see whether XML editors are smarter (or at least more compliant) in
this regard than their old-SGML counterparts.

This one feature probably makes implementation of an efficient, friendly
XML editor harder than most of the features that were eliminated from SGML
(omittag, shorttag and rank put together are comparatively trivial...).
The other hard feature is entity references in attribute values (yipes!
try to make a simple, friendly MFC dialog box that handles *that*
properly).

 Paul Prescod  - http://itrc.uwaterloo.ca/~papresco

"Perpetually obsolescing and thus losing all data and programs every 10
years (the current pattern) is no way to run an information economy or
a civilization." - Stewart Brand, founder of the Whole Earth Catalog
http://www.wired.com/news/news/culture/story/10124.html


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