DTD Attribute Types - IDREF
The attribute type of
IDREF is used for referring to an
ID value of another element in the document.
Valid XML - The following XML document would be valid, as it conforms to the above DTD:
Invalid XML - The following XML document would be invalid. This is because the
manager_id attribute of the second element contains a value that isn't the same as a value of another element that contains an attribute with a type of