words (RE: extensibility in XSchema?)

Rick Jelliffe ricko at allette.com.au
Tue Jun 23 16:23:50 BST 1998

> From: John E. Simpson

> Peter, I think you've got a bootstrapping problem here (or an illustration
> of Godel's theorem :). XML, like SGML, explicitly separates considerations
> of presentation from those of content ("presentation" covering a whole
> gamut of "things you can or should DO with this content"). It seems to me
> that you're asking for some generic way of making the separation go away,
> no? But shouldn't this be *impossible* under the very terms by which XML
> makes its way in the world?

No, because the processing instructions are just as much a part of XML (and
SGML) as elements. In the early days of SGML there was a lot of polemic
against PIs, to correct the prevailing RTF/TeX view--you can see from Steve
N's recent comments that the concern to stop XML people from confusing
generic markup with procedural markup is very strong still. Similarly there
is still a reductionist view that we just need elements for everything: that
PIs and entity references are impure or inelegant.

There is a currently a way to bind a PI to an element:
<!ENTITY x "<?RJ take this and shove it ?>" >
<object  PI="x">A wooden horsey</object>

Thus I think you can make that "separation" go away. But it does not
compromise the element structure of the document.

What Peter is asking, I think, is for some agreed on PI notation which can
be used to launch particular applications, based on an attribute in them.
This is no different than
	<?xml:stylesheet href="www.blah/blah" type="application/java"
	<?xml:stylesheet href="www.blort/blort" type="text/css" title="Simple" ?>

But rather than just being limited to just stylesheets to be run in the
current browser, he wants to be able to invoke other browsers.

This is already under W3C consideration: see James Clark's note on
stylesheets http://www.w3.org/TR/NOTE-xml-stylesheet.

Rick Jelliffe

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