11.3 Shorthand Pointers

     

XPointers provide a number of convenient extensions to XPath. One of the simplest is the shorthand pointer . A shorthand pointer is similar to an HTML named anchor; that is, a shorthand pointer identifies the element it's pointing to by that element's ID. The ID is supplied by an ID type attribute of the element being pointed at rather than by a special a element with a name attribute. To link to an element with a shorthand pointer, append the usual fragment separator # to the URL followed by the ID of the element to which you're linking. For example, http://www.w3.org/TR/1999/REC-xpath-19991116.xml#NT-AbsoluteLocationPath links to the element in the XPath 1.0 specification that has an ID type attribute with the value NT-AbsoluteLocationPath .

The ID attribute is an attribute declared to have an ID type in the document's DTD. It does not have to be named ID or id . Shorthand pointers cannot be used to link to elements in documents that don't have DTDs because such a document cannot have any ID type attributes.

The inability to use IDs in documents without DTDs is a major shortcoming of XML. Work is ongoing to attempt to remedy this, perhaps by defining a generic ID attribute such as xml:id or by defining a namespace that identifies ID type attributes.


For example, suppose you wanted to link to the Motivation and Summary section of the Namespaces in XML recommendation at http://www.w3.org/TR/1999/REC-xml-names-19990114/xml- names .xml. A quick peek at the source code of this document reveals that it has an id attribute with the value sec-intro and that indeed this attribute is declared to have an ID type in the associated DTD. Its start-tag looks like this:

 <div1 id='sec-intro'> 

Thus, http://www.w3.org/TR/1999/REC-xml-names-19990114/xml-names.xml#sec-intro is a URL that points to this section. The name does not need to be (and indeed should not be) enclosed in xpointer( ) to make this work. Just the ID value is sufficient. This is basically just a convenient shorthand for an XPointer built around an XPath expression using the id( ) function. The same URL could have been written as http://www.w3.org/TR/1999/REC-xml-names-19990114/xml-names.xml#xpointer(id(sec-intro)) .



XML in a Nutshell
XML in a Nutshell, Third Edition
ISBN: 0596007647
EAN: 2147483647
Year: 2003
Pages: 232

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