(d) an amendment, endorsement or addition has been made to or inserted in the travel document by any person other than an official duly authorized to do so; and, if he does so, shall, unless he returns it to the lawful holder thereof, transmit the travel document to the authority which issued it or on behalf of which it was issued. PART VI ALIENS 29 Additional restrictions on immigration of aliens (1) Subject to this section and without derogation from section thirteen, an alien shall not enter, be or remain in Zimbabwe unless he is in possession of—