code: public String evaluate(String expression, Object item)
          throws XPathExpressionException {
          return (String)this.evaluate( expression, item, XPathConstants.STRING );
      }
docs: <p>Evaluate an XPath expression in the specified context and return the result as a <code>String</code>.</p>
  
  <p>This method calls {@link #evaluate(String expression, Object item, QName returnType)} with a <code>returnType</code> of
  {@link XPathConstants#STRING}.</p>
  
  <p>See "Evaluation of XPath Expressions" of JAXP 1.3 spec
  for context item evaluation,
  variable, function and QName resolution and return type conversion.</p>
  
  <p>If a <code>null</code> value is provided for
  <code>item</code>, an empty document will be used for the
  context.
  If <code>expression</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>
  
  @param expression The XPath expression.
  @param item The starting context (node or node list, for example).
  
  @return The <code>String</code> that is the result of evaluating the expression and
  converting the result to a <code>String</code>.
  
  @throws XPathExpressionException If <code>expression</code> cannot be evaluated.
  @throws NullPointerException If <code>expression</code> is <code>null</code>.