[container.node.modifiers]
23 Containers library [containers]
23.2 Requirements [container.requirements]
23.2.5 Node handles [container.node]
23.2.5.5 Modifiers [container.node.modifiers]
constexpr void swap(node-handle& nh)
noexcept(ator-traits::propagate_on_container_swap::value ||
ator-traits::is_always_equal::value);
Preconditions: !alloc_ is true, or !nh.alloc_, or ator-traits::propagate_on_container_swap::value is true, or alloc_ == nh.alloc_ is true.