Document that all arguments with the same name in all methods should have the same type

This is important because if we can have multiple types of produce methods, we have to be able to pass arguments to them. But ideally, we would want that the whole primitive takes a set of inputs as a whole, which we can then map to methods. By having in fact arguments per primitive and not per method, we can achieve this. But then arguments have to be the same across all methods.