C++ named requirements: UnorderedAssociativeContainer (since C++11)

Unordered associative containers are Containers that provide fast lookup of objects based on keys. Worst case complexity is linear but on average much faster for most of the operations.

# Defect reports

DRApplied toBehavior as publishedCorrect behavior
LWG 2156C++11the load factor after rehashing could only bestrictly lower than the maximum load factorallowed to be equal