21 Containers library [containers]

21.2 Container requirements [container.requirements]

21.2.5 Insert return type [container.insert.return]

The associative containers with unique keys and the unordered containers with unique keys have a member function insert that returns a nested type insert_­return_­type.
That return type is a specialization of the template specified in this subclause.
template<class Iterator, class NodeType>
struct insert-return-type
{
  Iterator position;
  bool     inserted;
  NodeType node;
};
The name insert-return-type is exposition only.
insert-return-type has the template parameters, data members, and special members specified above.
It has no base classes or members other than those specified.