XML in a Nutshell, 3rd Edition

Locators

Each locator element has an xlink:type attribute with the value locator and an xlink:href attribute containing a URI for the resource it locates. For example, this novel element for The Wonderful Wizard of Oz contains three locator elements that identify particular editions of the book:

<novel xlink:type = "extended">
  <title>The Wonderful Wizard of Oz</title>
  <author>L. Frank Baum</author>
  <year>1900</year>
  <edition xlink:type="locator" xlink:href="urn:isbn:0688069444" />
                  <edition xlink:type="locator" xlink:href="urn:isbn:0192839306" />
                  <edition xlink:type="locator" xlink:href="urn:isbn:0700609857" />
</novel>

Most of the time each locator element also has an xlink:label attribute that serves as a name for the element. The value of this attribute can be any XML name that does not contain a colon (i.e., that does not have a namespace prefix). For instance, in the previous example, we could add labels based on the ISBN number, like this:

<novel xlink:type = "extended">
  <title>The Wonderful Wizard of Oz</title>
  <author>L. Frank Baum</author>
  <year>1900</year>
  <edition xlink:type="locator" xlink:href="urn:isbn:0688069444"
                                xlink:label="ISBN0688069444"/>
  <edition xlink:type="locator" xlink:href="urn:isbn:0192839306"
                                xlink:label="ISBN0192839306"/>
  <edition xlink:type="locator" xlink:href="urn:isbn:0700609857"
                                xlink:label="ISBN0700609857"/>
</novel>

The number alone cannot be used because XML names cannot start with digits. In this and most cases, the labels are unique within the ...