Flexible depth of navigation in block

Depth of the navigation is set to 5. For complex books, this is not enough. -> Flexible.

replace
Line 138:
$block['content'] = outline_page_menu_tree($this_node->volume_id,$path[0]->nid, 5, $expand);
with
$block['content'] = outline_page_menu_tree($this_node->volume_id,$path[0]->nid, variable_get('navigation_depth',5), $expand);

in the function outline_admin_settings add the following form field:

$form['navigation_depth'] = array(
'#type' => 'select',
'#title' => t('Depth of the navigation index being displayed in the block'),
'#default_value' => variable_get('navigation_depth',5),
'#options' => drupal_map_assoc(array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11,12)),
);

This gives you an other settings in the admin of outline.