Construct a EqualCollationKey function object that uses the collator
object for the current default locale to compare operands that are not
instances of CollationKey.
Return a range whose first element is an iterator positioned
at the first occurence of a specific key and whose second element is an
iterator positioned immediately after the last occurence of that key.
Return a range whose first element is an iterator positioned
at the first occurence of a specific object and whose second element is an
iterator positioned immediately after the last occurence of that object.