Bare Names (XML in a Nutshell, 2nd Edition)

11.3. Bare Names

XPointers provide a number of convenient extensions to XPath. One of the simplest is the bare name. A bare name XPointer is similar to an HTML named anchor; that is, a bare name XPointer identifies the element at which it's pointing by its name. However, this name 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 bare name, append the usual fragment separator # to the URL followed by the ID of the element to which you're linking. For example, the URL 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 ID type in the document's DTD. It does not have to be named ID or id. Bare names cannot be used to link to elements in documents that don't have DTDs because such a document cannot have any ID type attributes.

TIP: The inability to use IDs in documents without DTDs or schemas 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 ID type in the associated DTD. Its start-tag looks like this:

<div1 id='sec-intro'>

Therefore, 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 using an XPath expression using the id( ) function. The same URL could just as easily have been written as http://www.w3.org/TR/1999/REC-xml-names-19990114/xml-names.xml#xpointer(id(sec-intro)).