Associative containers provide an ability for optimized retrieval of data based on keys.
Associative container are parameterized on Key and an ordering relation. Furthermore, map and multimap associate an arbitrary type T with the key.
The phrase "equivalence of keys" means the equivalence relation imposed by the comparison and not the operator == on keys.
An associative container supports both unique keys as well as support fir equivalent keys.
An iterator of an associative container must be of the bidirectional iterator category.
The insert members shall not affect the validity of iterators.
Iterators of associative containers iterate through the containers in the non-descending order of keys where non-descending is defined by the comparison that was used to construct them.