CollectorPath: path,
		Descriptors:   descriptors,
		bucketLoader:  loader,
	}
	mg.validate()
	return mg
}

// AddExtraLabels - adds extra (constant) label KV pairs to the metrics group.
// This is a helper to initialize the `ExtraLabels` field. The argument is a
// list of ordered label name and value pairs.
func (mg *MetricsGroup) AddExtraLabels(labels ...string) {
	if len(labels)%2 != 0 {