code: public static ByteBuffer asByteBuffer(String expression, Node node)
              throws XPathExpressionException {
          return asByteBuffer(expression, node, xpath());
      }
docs: Evaluates the specified xpath expression, base64 decodes the data and
  returns the result as a ByteBuffer.
  <p>
  This method can be expensive as a new xpath is instantiated per
  invocation. Consider passing in the xpath explicitly via {
  {@link #asDouble(String, Node, XPath)} instead.  Note {@link XPath} is
  not thread-safe and not reentrant.
  
  @param expression
  The Xpath expression to evaluate.
  @param node
  The node on which to evaluate the expression.
  
  @return A ByteBuffer of base64 decoded data from the result of evaluating
  the specified Xpath expression.
  
  @throws XPathExpressionException
  If there are any problems evaluating the Xpath expression.