+ * by making sure all labels are the same in each position.
+ *
+ * We also only need to check the label values, because the label names are
+ * the same for all metrics in a metric family.
+ *
+ * 3 labels:
+ * [0] $plugin="$plugin_instance" => $plugin is the same within a family
+ * [1] type="$type_instance" => "type" is a static string
+ * [2] instance="$host" => "instance" is a static string
+ *
+ * 2 labels, variant 1:
+ * [0] $plugin="$plugin_instance" => $plugin is the same within a family
+ * [1] instance="$host" => "instance" is a static string
+ *
+ * 2 labels, variant 2:
+ * [0] $plugin="$type_instance" => $plugin is the same within a family
+ * [1] instance="$host" => "instance" is a static string
+ *
+ * 1 label:
+ * [1] instance="$host" => "instance" is a static string
+ */