[section:comparison Comparison to Associative Containers]

* The elements in an unordered container are organised into buckets, in an
  unpredictable order. There are member functions to.... TODO
* The unordered associative containers don't support the comparison operators.
* Instead of being parameterized by an ordering relation `Compare`,
  the unordered associative container are parameterized by a function object
  `Hash` and an equivalence realtion `Pred`. The member types and accessor
  member functions reflect this.
* Because of this, equivalent keys for unordered container are defined in
  terms of `Pred`, while for the associative containers it's defined in terms
  of `Compare`.
* Unordered associative containers' iterators can be invalidated by rehashing
  or by inserting elements.
* Unordered associative containers' iterators are of at least the forward
  iterator category. Associative containers' iterators are bidirectional.
* The unordered associative containers' constructors have extra parameters
  for the number of buckets, the hash function and the equality predicate.
* The unordered associative container don't have a `lower_bound` or
  `upper_bound` method - they wouldn't make any sense since the elements
  aren't ordered.
* TODO: Complexity guarantees.
* TODO: Behaviour when exceptions throw. The unordered containers seem
  a lot stronger defined here?

[endsect]