I just noticed that std::map and std::set have the member function equal_range returning an iterator range of values for a certain key. How does this make sense when a map and a set are always ordered key/value (as in a single key for a single value, or both combined) containers.

I would expect this member function with std::multimap and std::multiset since both of these allow for multiple values sharing the same key, and of course they both do. What am I missing?