Holds down the left mouse button on the source element,
           then moves to the target offset and releases the mouse button.

        :Args:
         - source: The element to mouse down.
         - xoffset: X offset to move to.
         - yoffset: Y offset to move to.

def drag_and_drop_by_offset(self, source, xoffset, yoffset):
        """
        Holds down the left mouse button on the source element,
           then moves to the target offset and releases the mouse button.

        :Args:
         - source: The element to mouse down.
         - xoffset: X offset to move to.
         - yoffset: Y offset to move to.
        """
        self.click_and_hold(source)
        self.move_by_offset(xoffset, yoffset)
        self.release()
        return self