code: function(value, nodeName, attributeName, attributeValue)
  	 {
  	 	if (value != null && !isNaN(value.nodeType) && (nodeName == null ||
  	 		value.nodeName.toLowerCase() == nodeName.toLowerCase()))
   		{
   			return attributeName == null ||
   				value.getAttribute(attributeName) == attributeValue;
   		}
  	 	
  	 	return false;
  	 }
docs: Function: isNode
  
  Returns true if the given value is an XML node with the node name
  and if the optional attribute has the specified value.
  
  This implementation assumes that the given value is a DOM node if the
  nodeType property is numeric, that is, if isNaN returns false for
  value.nodeType.
  
  Parameters:
  
  value - Object that should be examined as a node.
  nodeName - String that specifies the node name.
  attributeName - Optional attribute name to check.
  attributeValue - Optional attribute value to check.