code: def xpath_eval(node, extra_ns=None):
      
      namespaces = {'bpmn': BPMN_MODEL_NS}
      if extra_ns:
          namespaces.update(extra_ns)
      return lambda path: node.findall(path, namespaces)
docs: Returns an XPathEvaluator, with namespace prefixes 'bpmn' for
      http://www.omg.org/spec/BPMN/20100524/MODEL, and additional specified ones