Extended links

Using an extended link, a number of resources can be cross-related. An extended link contains locator elements, each one pointing to a different resource. However, the extended link may still be an in-line element, containing one of the resources:

The ends of the link have equal status, even if one resource is a single word reference and the other is an entire book. It is also irrelevant which end of the link actually contains the linking markup.

Extended type

Extended links refer to a number of resources by including embedded resource locators. Each locator is stored in a locator-type element, and all related locator elements are grouped within an extended-type element. If the link markup occurs at the point of one of the resources to be included, then a resource-type element is used to isolate and identify this (local) resource. The Type attribute is again used to identify the elements that take these roles.

A DTD author must ensure that the extended-type element can contain the locator-type element and the resource-type element, as well as any DTD-specific elements appropriate at this point:

<!ELEMENT para       (#PCDATA | extendedLink | emph)* >

<!ELEMENT extendedLink   (#PCDATA | localResource |
                          remoteResource | emph)* >
<!ATTLIST extendedLink   xlink:type="extended" ... >

<!ELEMENT localResource  (#PCDATA) >
<!ATTLIST localResource  xlink:type="resource" ... >

<!ELEMENT remoteResource (#PCDATA) >
<!ATTLIST remoteResource xlink:type="locator" ... >

   <para>Here are
     <extendedLink>some <emph>extended</emph>
       <localResource>links:</localResource>
						<remoteResource xlink:href="...">
         Locator a
       </remoteResource>,
						<remoteResource xlink:href="...">
         Locator b
       </remoteResource>.
						</extendedLink>
   </para>

                 Here are some extended links: Locator a, Locator b.

A browser should recognize that the embedded LocalResource and RemoteResource elements form a related group, and deduce that it would be useful to dynamically create arcs between them all (in this case, between the fragment shown above;, the fragment identified as 'Locator a' and the fragment identified as 'Locator b'.

Empty links

The example link above creates three resources (one local, two remote). But it is possible for a link to contain a single, local resource, or even to contain no resources at all. This might be done simply to utilize XLink identification attributes that give the resource a role, title or label, or to create a placeholder for later updating.