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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: RE: Namespaces Best Practice
 <Tony.Coates@r...> wrote: > I was told that the XSLT spec is likely to tighten up to stop processors from trying to > put all namespace declarations at the top. There are two reasons for this. One is > for performance, as mentioned in a previous post. The other is that namespace > prefixes are allowed to be re-used in different parts of a document for different > namespaces, and XSLT is sensitive to the prefix as well as the namespace, so > there is no (simple) general mechanism by which you actually can move all > namespace declarations to the top in all possible cases. Actually there is a simple straightforward algorithm to do this exact thing (in the non-streaming case). Algorithm to normalize namespace prefixes During the parse phase phase, build a map of prefix/namespaceURI bindings. Remove all duplicate prefix/namespaceURI bindings by only using the first prefix declared on a namespaceURI and renaming any prefix declared on a namespaceURI already in the map. During the serialization phase, emit the prefix/ns bindings at xmlns attributes of the root element. As each element/attribute is emitted, lookup the prefix from the node's namespaceURI in the map. In the frequent case where a document is parsed, processed and emitted, this algorithm adds negligable overhead. > > Of course, you can argue that it might be poor practice to re-use namespace prefixes in this way, but XSLT processor authors shouldn't be asked to get into the business of only supporting those documents that they consider exemplars of "good practice". Programming language processors need to accept all legal forms of a language ... on the other hand people who need to debug programs, or read XML documents, do appreciate such good practices. I suspect that if we were to run a "delibately obfuscated XML" contest, documents employing heavy prefix overloading and mixed use of qualified and unqualified -unprefixed- elements would carry the day. Jonathan 
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