The fact that Anglophone countries don't have language regulator bodies id mind-boggling.
Basically schools marking down your work for mistakes can't refer to anything as the source of truth other than "this private entity, sometimes in a foreign country, published a book that says so" or just "it's common knowledge".
Basically schools marking down your work for mistakes can't refer to anything as the source of truth other than "this private entity, sometimes in a foreign country, published a book that says so" or just "it's common knowledge".