The specification of the try_emplace and insert_or_assign member functions in N4279 contains the following errors and omissions:
In insert_or_assign, each occurrence of std::forward<Args>(args)... should be std::forward<M>(obj); this is was a mistake introduced in editing.
In try_emplace, the construction of the value_type is misspecified, which is a mistake that was introduced during the evolution from a one-parameter to a variadic form. As written, value_type(k, std::forward<Args>(args)...) does not do the right thing; it can only be used with a single argument, which moreover must be convertible to a mapped_type. The intention is to allow direct-initialization from an argument pack, and the correct constructor should be value_type(piecewise_construct, forward_as_tuple(k), forward_as_tuple(std::forward<Args>(args)...).
Both try_emplace and insert_or_assign are missing requirements on the argument types. Since the semantics of these functions are specified independent of other functions, they need to include their requirements.