code: def child_at_index(self, name, index):
          
  
          def _finder(n, i):
              try:
                  return self.indexes[n][i]
              except (KeyError, IndexError):
                  try:
                      return self.traversal_indexes[n][i]
                  except (KeyError, IndexError):
                      return None
  
          child = _finder(name, index)
          child_name = None if name is None else self._find_name(name)
          if child_name != name:
              child = _finder(child_name, index)
          return child
docs: Return the child named `name` at the given index
  
          :type name: ``str``
          :param name: child name (e.g. PID)
  
          :type index: ``int``
          :param index: child index
  
          :return: an instance of :class:`Element <hl7apy.core.Element>` subclass