docs: def _submit_rate(self, metric_name, val, metric, custom_tags=None, hostname=None):
          """
          Submit a metric as a rate, additional tags provided will be added to
          the ones from the label provided via the metrics object.
  
          `custom_tags` is an array of 'tag:value' that will be added to the
          metric when sending the rate to Datadog.
          """
          _tags = self._metric_tags(metric_name, val, metric, custom_tags, hostname)
          self.rate('{}.{}'.format(self.NAMESPACE, metric_name), val, _tags, hostname=hostname)