 co-ordinate following.
        </td>
      </tr>
      <tr>
	<td valign="top">
	<tt>PREVLEFT</tt>
	</td>
	<td valign="top">
        Previous items left co-ordinate. 
        </td>
      </tr>
      <tr>
	<td valign="top">
	<tt>PREVRIGHT</tt>
	</td>
	<td valign="top">
        Previous items right co-ordinate. 
        </td>
      </tr>
      <tr>
	<td valign="top">
	<tt>PREVTOP</tt>
	</td>
	<td valign="top">
        Previous items top co-ordinate. 
        </td>
      </tr>
      <tr>
	<td valign="top">
	<t