docs: def restricted_registry(self, names):
          """Returns object that only collects some metrics.
  
          Returns an object which upon collect() will return
          only samples with the given names.
  
          Intended usage is:
              generate_latest(REGISTRY.restricted_registry(['a_timeseries']))
  
          Experimental."""
          names = set(names)
          collectors = set()
          with self._lock:
              for name in names:
                  if name in self._names_to_collectors:
                      collectors.add(self._names_to_collectors[name])
          metrics = []
          for collector in collectors:
              for metric in collector.collect():
                  samples = [s for s in metric.samples if s[0] in names]
                  if samples:
                      m = Metric(metric.name, metric.documentation, metric.type)
                      m.samples = samples
                      metrics.append(m)
  
          class RestrictedRegistry(object):
              def collect(self):
                  return metrics
  
          return RestrictedRegistry()