def rotate(self):
        """ Rotate the kill ring, then yank back the new top.
        """
        if self._prev_yank:
            text = self._ring.rotate()
            if text:
                self._skip_cursor = True
                cursor = self._text_edit.textCursor()
                cursor.movePosition(QtGui.QTextCursor.Left,
                                    QtGui.QTextCursor.KeepAnchor,
                                    n = len(self._prev_yank))
                cursor.insertText(text)
                self._prev_yank = text
Rotate the kill ring, then yank back the new top.