PIs in xml:schema
Don Park wrote: > > I entirely agree with your opinion. Liam's view is that of concern over > misuse where I am more concerned with functionality. I believe XML > community can benefit from a guideline for proper use of PI as well as some > mechanism for registering PI target names. Meanwhile we need to encourage > HTML browsers to recognize PI so that we do not lose this important feature > of XML. Let me reiterate that in my mind the best way to handle this would be to allow these floating element types in XML schemas. So in a sense I am for the removal of PIs ... once they are properly replaced. I can think of an element-syntax replacement that would be far superior. Here is the beginning of a specification: The big problem with PIs is that they are not declared, namespace managed or internally structured (according to XML). Our replacement would have to allow a document to declare that it was using XHTML with "style binding inclusion extensions" or "xyz formatter page break extensions" or "zyx editor cursor position extensions". The fundamental characteristic of a floating element type is that an application that did not know about the floating element type could choose not to see elements of that type or their content. In this case the term "application" includes stylesheets and schemas. Further, it should be possible to identify a floating element type without reading the document's schema(s) -- or even reading the schema for the element type. As a very (very) rough strawperson proposal, lets say that we have a declaration: <mydoc xmlfloat:ns="http://.../someschema.xsd"> This syntax should be aligned with a) the NS spec, b) the xml:schema declaration syntax and c) the xml:schema ns/schema importation syntax. For now, we'll use this syntax. This declaration would say: a) elements in this namespace are floating elements b) they should conform to the referenced schema Floating elements would be invisible to the "main" schema and to each other. So conceptually a different instance of the schema processor would be required for each included schema. Some layer between SAX and a "float smart" application (including an XSL processor, XML Schema validator or DOM engine) would filter out floating elements that had not been specifically requested. You could register with the layer what floating elements you are interested in or simply ask for all of them. Stylesheets would register for the floating elements that they are interested in and only see those and no others. This is superior to PIs because today PIs mess up things like node-list-first...you might think that the title of a chapter would be its first node but not if there is a PI there! DOM-based applications would register recognized float schemas with the DOM-constructor (or ask for them all). Helper functions/methods would allow filtering at runtime. If we had all of this then I don't see why we would need the "<?" in the document. An author doesn't really care whether a particular element is a floating element or not. So we could dump PIs as-we-know-them. Why are floating elements better than PIs? * they would have a schema language * they would reuse element syntax (more consistent) * they could contain XML-defined sub-elements * their namespace would be managed * their basic syntax is already standardized (as XML 1.0 elements) I think that this is superior to PIs. Note: SGML's inclusions have a bad reputation because they can be applied at any point in a document type. That means that if you move a paragraph from one place to another its validity could change based on its content. It is arguable whether this is a good idea. Plus there is no standardized way to filter them out. -- Paul Prescod - ISOGEN Consulting Engineer speaking for only himself http://itrc.uwaterloo.ca/~papresco Earth will soon support only survivor species -- dandelions, roaches, lizards, thistles, crows, rats. Not to mention 10 billion humans. - Planet of the Weeds, Harper's Magazine, October 1998 xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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