XML Companion, The, Third Edition

ID/IDREF

The XML standard relies upon the two special attribute types, 'ID' and 'IDREF', to identify attributes that serve as the target and source of a link. Using this technique, the target object must be enclosed by an element that has an attribute defined to be of type ID. A unique value must be placed in this attribute:

<!ELEMENT section (...) >
<!ATTLIST section target
					ID #REQUIRED>
   <section target="S6">
     <title>This is Section 6</title>
     ...
     ...
     ...
   </section>

Every reference must be contained within an element that has an attribute defined to be of type IDREF. For example, a referencing element called 'XRef' may use an attribute called 'Link' to point to the required element:

<!ELEMENT xref (...) >
<!ATTLIST xref link IDREF #REQUIRED> ...