Is the wiping mentioned in the sleeping adhkār (supplications) actually on the body or on the clothes?

The Prophet, may Allah's prayers and peace be upon him, used to recite the Mu'awwidhat (Surahs Al-Falaq and An-Nas) before sleeping, then blow into his hands and wipe with them as much of his body as he could, starting with his head and face. He would do this three times. It appears that the wiping should be directly on the body, but it is also permissible to wipe over clothes, and there is latitude in this matter.