Role...permission i.e. panel.page.visibility

No (php) error message but “Du darfst dies nicht tun” if the editor hit “save”.
The changes are saved anyway,

Here is my “roles” snippet:

   ...
   'panel.page.visibility' => function() {
  //error_log($this->target()->page()->template());
  //error_log( print_r( $this->target(), true ) );
  //error_log($this->state());

  if($this->target()->page()->template() === 'page') {
    return false;
  } else {
    return true;
  }
},
...

I think the “visibility” is a part of the normal save-flow and so the permission-exception kicks in.

S.