RE: [xsl] XSLT 1.0 support in browsers

Subject: RE: [xsl] XSLT 1.0 support in browsers
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Wed, 02 May 2007 10:52:58 -0400
At 05:18 PM 5/1/2007, Mike wrote:
> <!DOCTYPE foo SYSTEM "whatever" [
> <!ATTLIST foo xml:space #IMPLIED>
> ]>
> <foo xml:space="preserve">
> ....
>

Ah yes, that lovely feature of DTDs - you can do your own thing, and still
be valid.

This isn't a problem, as long as you define "validity" accordingly. (I.e., in a way that might nullify its practical usefulness in pathological cases. But what technology is immune from pathology?)


By making DTDs formally optional for parsing, XML took a big step away from SGML -- bigger than many engineers seem to have understood at the time. If MS had done the right thing at the start and not decided it was safe to throw away whitespace arbitrarily, this never would have been a problem. Even apart from xml:space (which is in essence a patch over a problem created when DTD parsing becomes optional), DTD content models offer valuable information about which whitespace is safe to throw away, which is why whitespace munging in the parse phase was thinkable under SGML. (Not that the MS parser uses this information. Its original developers seem not to have thought about mixed content.) But in XML, the DTD is not always there, and the decision of which whitespace is "significant" or not becomes subject to unpredictable interactions between document instances (which may or may not invoke DTDs) and processing architectures (which may or may not parse them even when invoked).

This is why well-behaved XML processors do not take it upon themselves to throw away whitespace without explicit say-so, and why XSLT had to go beyond its purview and hope, impossibly, to dictate upstream processor behavior: "Please don't throw away whitespace; I can take care of it".

Cheers,
Wendell


====================================================================== Wendell Piez mailto:wapiez@xxxxxxxxxxxxxxxx Mulberry Technologies, Inc. http://www.mulberrytech.com 17 West Jefferson Street Direct Phone: 301/315-9635 Suite 207 Phone: 301/315-9631 Rockville, MD 20850 Fax: 301/315-8285 ---------------------------------------------------------------------- Mulberry Technologies: A Consultancy Specializing in SGML and XML ======================================================================

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