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Re: [xml-dev] SGML default attributes.


(catching up ...)

On 29 Apr 2016, at 17:58, John Cowan wrote:

On Fri, Apr 29, 2016 at 8:54 AM, Norman Gray <norman@astro.gla.ac.uk> wrote:

In the XML world, the DTD is just for validation

That turns out not to be the case. There are a number of XML DTD features
which affect the infoset returned by a compliant parser. If they are in
the internal subset, the parser MUST respect them;
I stand corrected; I was sloppy. I think this doesn't change my original point, however, which was that in SGML the DTD was integral to the document, and to the parse of the document, and that it's easy to forget this after one has got used to two decades of XML[1]. I can't remember if there was a trivial or default DTD which was assumed in the absence of a declared one, in the same way that there was a default SGML Declaration, but taking advantage of that would probably have been regarded as a curiosity, rather than normal practice.

In XML, in contrast, the DTD has a more auxiliary role, and at a first conceptual look, that role is validation (even though -- footnote! -- it may change other things about the parse as well). Thus _omitting_ an XML DTD (or XSchema) is neither perverse nor curious.

Practical aspect: When I'm writing XML, I use a DTD (in whatever syntax) to help Emacs tell me if the document is valid, but I don't even know whether the XML parsers I use are capable of using a DTD external subset. That careless ignorance would be impossible with SGML.

The rational extension of that attitude, of course, is MicroXML, which (as you of course know) doesn't use any external resources at all, and doesn't care about validation.

Best wishes,


[1] Hang on, _two_ decades?! I've just checked and ... 1996 doesn't seem that long ago.

Norman Gray : https://nxg.me.uk
SUPA School of Physics and Astronomy, University of Glasgow, UK

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