enum SlotFlags

Slots that reference scope variables (v-for or an outer slot prop), or has conditional structure (v-if, v-for). The parent will need to force the child to update because the slot does not fully capture its dependencies.

<slot/> being forwarded into a child component. Whether the parent needs to update the child is dependent on what kind of slots the parent itself received. This has to be refined at runtime, when the child’s vnode is being created (in normalizeChildren)

Stable slots that only reference slot props or context state. The slot can fully capture its own dependencies so when passed down the parent won’t need to force the child to update.