Placeholder — one shape, whatever the value turns out to be
Union — one shape per type, chosen branch by branch
The same forms stand as the non-projection half of a Slot. Cardinality sits on the side: a binding yields
one value per row and a template entry one per property value, so neither nests a Projection.
Projection value model.
The value a Projection binding takes:
The same forms stand as the non-projection half of a Slot. Cardinality sits on the side: a binding yields one value per row and a template entry one per property value, so neither nests a
Projection.