Yes, this is allowed. The present-status of optional arguments is carried through. I am not sure why you call this "careless", it can be a very useful property. It does require that an explicit interface be visible at all steps.
See the additional topic "Optional Arguments" that is referenced at the bottom of the OPTIONAL page. The description of OPTIONAL is about the syntax term - the concept of omitted arguments is more complex and discussed elsewhere. I'll also comment that the compiler reference is not intended as a tutorial on the language.