For the sake of exposition, Clauses [language.support] through [thread] and Annex [depr] do not describe copy/move constructors, assignment operators, or (non-virtual) destructors with the same apparent semantics as those that can be generated by default ([class.ctor], [class.dtor], [class.copy]). It is unspecified whether the implementation provides explicit definitions for such member function signatures, or for virtual destructors that can be generated by default.
For the sake of exposition, the library clauses sometimes annotate constructors with EXPLICIT. Such a constructor is conditionally declared as either explicit or non-explicit ([class.conv.ctor]). [ Note: This is typically implemented by declaring two such constructors, of which at most one participates in overload resolution. — end note ]