ameters:</B><DD><CODE>source</CODE> - The <code>InputSource</code> of the document to evaluate over.<DT><B>Returns:</B><DD>The <code>String</code> that is the result of evaluating the expression and converting the result to a
   <code>String</code>.<DT><B>Throws:</B><DD><A HREF="../../../../javax/xml/xpath/XPathExpressionException.html">XPathExpressionException</A> - If the expression cannot be evaluated.<DD>java.lang.NullPointerException - If  <code>source</code> is <code>null</code>.</DL>
</DD>
</DL>
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