(DTD) governing this
 kind of document.
 <P>
 If the attribute has not been explicitly assigned a value, but has
 been declared in the DTD, it will exist and have that default. Only
 if neither the document nor the DTD specifies a value will the
 Attribute really be considered absent and have no value; in that
 case, querying the attribute will return null.
 <P>
 Attributes may have multiple children that contain their data. (XML
 allows attributes to contain entity references, and tokenized
 attribute type