DTD Attribute Types - IDREFS
The attribute type of
IDREFS is used for referring to the
ID values of more than one other element in the document. Each value is separated by a space.
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