[flat.{map,multimap,set,multiset}] "Empty" used as a verb

[frederick-vs-ja]

In the current wording for flat container adaptors, sometimes "empty" is used as a verb (in the form "emptied"). This seems somehow unconventional and inconsistent with empty functions in the standard library.

Should we switch to use "cleared" for the consistency with clear functions?

[jwakely]

For the postconditions of extract() I think it would be better to say that empty() is true. For the notes about "being emptied", I think that usage is OK: the container being emptied means it is made empty, i.e. it is made so that empty() is true. Google's definition is literally "remove all the contents of (a container)."