docs: def path(self, target, args, kw):
          """Build a URL path fragment for a resource or route.
  
          Possible values for `target`:
  
          A string that does not start with a '.' and does not contain ':'.
            : Looks up the route of the same name on this mapper and returns it's
              path.
  
          A string of the form 'a:b', 'a:b:c', etc.
            : Follows the route to nested mappers by splitting off consecutive
              segments. Returns the path of the route found by looking up the
              final segment on the last mapper.
  
          A `Route` object
            : Returns the path for the route.
  
          A resource that was added previously
            : Looks up the first route that points to this resource and
              returns its path.
          """
          if type(target) in string_types:
              if ':' in target:
                  # Build path a nested route name
                  prefix, rest = target.split(':', 1)
                  route = self.named_routes[prefix]
                  prefix_params = route._pop_params(args, kw)
                  prefix_path = route.path([], prefix_params)
                  next_mapper = route.resource
                  return prefix_path + next_mapper.path(rest, args, kw)
              else:
                  # Build path for a named route
                  return self.named_routes[target].path(args, kw)
          elif isinstance(target, Route):
              # Build path for a route instance, used by build_url('.')
              for route in self.routes:
                  if route is target:
                      return route.path(args, kw)
              raise InvalidArgumentError("Route '%s' not found in this %s object." % (target, self.__class__.__name__))
          else:
              # Build path for resource by object id
              target_id = id(target)
              if target_id in self._lookup:
                  return self._lookup[target_id].path(args, kw)
              raise InvalidArgumentError("No Route found for target '%s' in this %s object." % (target, self.__class__.__name__))