Use Page::listable to restrict visibility of pages throughout admin

[Toutouwai]

Short description of the enhancement

You can hook Page::listable and set the event return to false to hide a page in ProcessPageList (from non-superusers). However, the page can still be discovered via:

• Admin search (AJAX results)
• Admin search (results page if user hits enter)
• Listers
• Maybe other places such as Page Reference fields?

It would be good if Page::listable could make a page invisible throughout the admin. Or if it's important to keep a targeted method just for ProcessPageList then introduce a new hookable method that controls visibility throughout the admin.

Why would the enhancement be useful to users?

The title or mere existence of a page might need to remain private from the current user.

[BernhardBaumrock]

Thx for opening that issue robin!

That need came up several times:
https://processwire.com/talk/topic/15854-how-to-hide-menu-item-in-the-backend/
https://processwire.com/talk/topic/22369-hide-uneditable-pages-in-admin-treeprocesspagelist/
https://processwire.com/talk/topic/10195-hide-pages-from-admin-tree/
https://processwire.com/talk/topic/24969-keeping-backend-data-private-from-peer-roles/

I'd love to have a proper way for doing this!