https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96821
--- Comment #2 from Daniil Dudkin <dudkindaniilm2 at yandex dot ru> --- Basically it described in 4th paragraph in [temp.constr.decl] of the latest C++ standard draft: http://eel.is/c++draft/temp.constr.decl#4
