24.3.2 describes struct iterator, which didn't exist in the
+ original HP STL implementation (the language wasn't rich enough at the
+ time). For backwards compatibility, base classes are provided which
+ declare the same nested typedefs:
+
input_iterator
output_iterator
forward_iterator
bidirectional_iterator
random_access_iterator
24.3.4 describes iterator operation distance, which takes
+ two iterators and returns a result. It is extended by another signature
+ which takes two iterators and a reference to a result. The result is
+ modified, and the function returns nothing.
+