Add a submenu tree in a block

Warning: does not work for menu 'node/add' trail but works for 'admin'. The test done was with a custom menu. So feedback is very welcome!

You can add an expanded submenu of the primary links by creating a block containing the following code.

The end result will be a block containing a submenu of the active menu. By using block visibility the block is only visible for the appropriate submenus.

1. Go to the admin/build/block/add page.
2. Paste the following code into the block body:
   
   <?php
$menu_trail= _menu_get_active_trail();
$menu_top_level = array_shift( $menu_trail);

// comment next line when finished testing using: // in front
print( 'top-level-id= ' . $menu_top_level .'<br/>');

$menu_sub_menu =  array_shift( $menu_trail);
print( menu_tree(  $menu_sub_menu));
?>
3. Be sure to check the PHP code.
4. Paste the following code into 'Page specific visibility settings':
   
   <?php
// Fill in the appropriate top level ID's in a comma-separated list
$valid_top_levels = array(1, 2);
// Uncomment next line when finished testing
//return in_array( array_shift( _menu_get_active_trail()), $valid_top_levels);
return TRUE;
?>
5. Enable the checkbox 'Show if the following PHP code returns TRUE (PHP-mode, experts only).'
6. Make the new block visible.
7. When satisfied, uncomment the line as indicated in the above PHP code