service and a ParsedXMLElement is
created, it is propogated to all filters and listeners. Any one of those
can consume the element to prevent its propogation to other filters or
listeners. This method marks the element as consumed.
Overrides to allow for directly accessing child elements and attributes. If
prefaced by attr_ it looks for an attribute that matches or checks for a
child with a tag that matches the method name. If no match occurs, it
returns a NilParsedXMLElement (singleton) instance.