Thank you very much. For the code from the docs it helped.
But my real problem was, that my tags
code
... // some code
'html' => function($tag) {
$subpages = $tag->parent()->children();
if($children == 'visible') {
$subpages = $subpages->visible();
} elseif($children == 'invisible') {
$subpages = $subpages->invisible();
}
... // some code
had some deprecated code, which I did not get reported although debug was enabled.
But that is another storry.
And I have this code now updatet too