Return a newly created `a:path` element added to *sp*.

        The returned `a:path` element has an `a:moveTo` element representing
        the shape starting point as its only child.

def _start_path(self, sp):
        """Return a newly created `a:path` element added to *sp*.

        The returned `a:path` element has an `a:moveTo` element representing
        the shape starting point as its only child.
        """
        path = sp.add_path(w=self._dx, h=self._dy)
        path.add_moveTo(
            *self._local_to_shape(
                self._start_x, self._start_y
            )
        )
        return path