+ /** Numeric symbol for this DataType.
+ *
+ * Castable to int for use as an array index (e.g. by ChanCount).
+ * Note this means NIL is (ntypes-1) and guaranteed to change when
+ * types are added, so this number is NOT suitable for serialization,
+ * network, or binary anything.
+ *
+ * WARNING: The number of non-NIL entries here must match num_types.
+ */