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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XML-appropriate editing data structures
 At 4:36 PM +0200 4/9/04, Henrik Martensson wrote: >Allowing authors to add tags not supported by the DTD (and therefore not >by the processing systems that are designed to support what the DTD >supports, nothing less, nothing more) renders the use of XML >meaningless. A common fallacy, and one I'm not surprised to hear from you given your avowed SGML background. The fundamental difference between XML and SGML is not the restricted syntax, and the one that means XML is not just a subset of SGML, is that XML separates the notion of well-formedness from validity. In XML, well-formedness is required. Validity isn't, and normally shouldn't be. A processing system that can only handle what the DTD mandates is flawed. Instead a processing system needs to ask if the document provides what it needs to do its job, not if it adheres to some arbitrary schema. And if the document doesn't provide what it needs, then the system should notice and handle the case gracefully, perhaps alerting a human, perhaps not, depending on circumstances. The DocBook XSL stylesheets, for example, still work quite well with invalid markup. Indeed, XPath and XSLT 1.0 based systems generally do work quite well with documents regardless of validity because those languages were designed without the assumption of validity. Sadly, the same cannot be said for many other systems that were needlessly tightly coupled to particular formats. Built here it is the systems that are broken. The X stands for extensible. When objects are encountered that are not represented in the current DTD/schema it is the right and duty of the author to invent new markup to describe what is actually there. Systems that cannot deal sensibly with the extensibility of XML are broken. -- Elliotte Rusty Harold elharo@m... Effective XML (Addison-Wesley, 2003) http://www.cafeconleche.org/books/effectivexml http://www.amazon.com/exec/obidos/ISBN%3D0321150406/ref%3Dnosim/cafeaulaitA 
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