provides attributes for filtering by an XPath predicate expression.the condition under which the element bearing this attribute applies, given as an XPath predicate expression.
The XPath predicate expression given as the value of the predicate
attribute has to be provided without wrapping square brackets.
If it is a child of a person element, treat as inline
The following example declares that the name element can be mapped to, or is equivalent to, the external
concepts of PERSON and PLACE depending on the XPath expression given in predicate