Slices a node's entry-major branch index down to the branches one variant shape contributes.
A node's Entries index every union variant's branches by property name; this cross-cuts
that index along the shape axis, keeping at each name the branches whose name shape declares. A path
crossing the union under a shared predicate folds to a single branch (§5.8.1) contributed by every
variant declaring that name, so such a branch surfaces under each of them.
Slices a node's entry-major branch index down to the branches one variant shape contributes.
A node's Entries index every union variant's branches by property name; this cross-cuts that index along the shape axis, keeping at each name the branches whose name
shapedeclares. A path crossing the union under a shared predicate folds to a single branch (§5.8.1) contributed by every variant declaring that name, so such a branch surfaces under each of them.