Clarify problem with copy and assign

Author: steve-downey

papers/P2988/optional_ref_wording.tex

@@ -389,7 +389,7 @@ \section{Assignment of optional<T\&>}
 This observation allows us to provide only copy-assignment for \tcode{optional<T\&>}, instead of a set of converting assignments, that would need to replicate the signatures of constructors and their constraints. Assignment from any other value is handled by first implicitly constructing \tcode{optional<T\&>} and then using copy-assignment. Move-assignment is the same as copy-assignment, since only pointer copy is involved.
 
 \section{Copy and Assignment of optional<U\&>\&\& to optional<T>}
-Care must be take to prevent the assignment of a movable optional to disallow the copy or assignment of the underlying referred to value to be stolen. The \tcode{optional<U\&> const\&} assignment or copy constructor should be used instead. We thank Jan Kokemüller for uncovering this bug.
+Care must be take to prevent the assignment of a movable optional to disallow the copy or assignment of the underlying referred to value to be stolen. The \tcode{optional<T>::optional<U\&> const\&} assignment or copy constructor should be used instead, which also needs to check slightly different constraints for \tcode{converts-from-any-cvref} and for testing \tcode{is_assignable}. We thank Jan Kokemüller for uncovering this bug. The bug seemns to be present in many optional implementations that support references.
 
 
 \chapter{Proposal}