code: func (q *querier) LabelValues(name string) ([]string, error) {
  	expressions := []string{"name=~[a-zA-Z_][a-zA-Z0-9_]*$"}
  	if name == model.MetricNameLabel {
  		name = "name"
  		expressions = append(expressions, "name=~[a-zA-Z_:][a-zA-Z0-9_:]*$")
  	}
  	return q.MetricIndex.FindTagValues(q.OrgID, name, "", expressions, 0, 100000)
  }
docs: // LabelValues returns all potential values for a label name.