Create an empty unordered multiset. Optionally specify an initialNumBuckets indicating the initial size of the array of buckets of this container. If initialNumBuckets is not supplied, a single bucket is used. Optionally specify a hashFunction used to generate the hash values for the keys contained in this unordered multiset. If hashFunction is not supplied, a default‐constructed object of the (template parameter) type HASH is used. Optionally specify a key‐equality functor keyEqual used to verify that two keys are equivalent. If keyEqual is not supplied, a default‐constructed object of the (template parameter) type EQUAL is used. Optionally specify a basicAllocator used to supply memory. If basicAllocator is not supplied, a default‐constructed object of the (template parameter) type ALLOCATOR is used. If the type ALLOCATOR is bsl::allocator (the default), then basicAllocator, if supplied, shall be convertible to bslma::Allocator *. If the type ALLOCATOR is bsl::allocator and basicAllocator is not supplied, the currently installed default allocator is used.