top">Yes.</td>
      </tr>
      <tr>
        <td valign="top">value</td>
        <td valign="top">The value to set the property to.</td>
        <td align="center" valign="top">No, if
           <code>operation</code> is specified.</td>
      </tr>
      <tr>
        <td valign="top">operation</td>
        <td valign="top">The operation to perform on the existing value.
           Possible values are "+" and "-", which add and subtract 1,
           respectively from the existing value.  If the value doesn