+/**
+ * \brief Lay out a dynamic \ref relation initializer for a relation
+ * wth the given column "types".
+ *
+ * This defines a \ref relation intializer that creates the \ref
+ * tupleschema for the given columns.
+ *
+ * \note The initializer cannot be used statically.
+ *
+ * The \b content \ref hashvector is a \ref nibble_index_level variant
+ * with an initial size of 16 slots.
+ *
+ * The constraints \ref vector is a \ref bitpair_index_level variant
+ * with initial size 0.
+ *
+ * The \b content \ref hashvector \b type is set up with an allocated
+ * \ref tupleschema that has an allocated \ref tuple that declares the
+ * column "types" view the given \ref itemkeyfun pointers. Any add
+ * constraints will need to clone that \ref tupleschema and then clear
+ * the column slots for the constraint value columns, typically by
+ * using \ref tupleschema_mask for this.
+ *
+ * \related relation
+ */
+#define RELATION(...) (relation) { \
+ .content = { \
+ .table = { .variant = nibble_index_levels, .size=16, .entries=0 }, \
+ .fill = 0, .holes = 0, \
+ .type = (itemkeyfun*) TUPLESCHEMA( __VA_ARGS__ ) \
+ }, \
+ .constraints = { .variant = bitpair_index_levels, .size=0, .entries=0 } \
+}
+