*    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 */
public int indexOf (CTableItem item) {
	checkWidget ();
	if (item == null) SWT.error (SWT.ERROR_NULL_ARGUMENT);
	if (item.parent != this) return -1;
	return item.index;
}