print string item0 to the current position and next strings to defined positions
        example: .header("Name", 75, "Quantity", 100, "Unit")

def header(self, item0, *items):
        """print string item0 to the current position and next strings to defined positions
        example: .header("Name", 75, "Quantity", 100, "Unit")
        """
        self.txt(item0)
        at_x = None
        for item in items:
            if at_x is None:
                at_x = item
            else:
                self.txt(item, at_x=at_x)
                at_x = None