Generally, it is best to manage permissions at the space level.
However, if you need to use page permissions, you must understand how space and page permissions work.
Space and page permissions analogy
Permissions are best understood using the analogy of a room (the wiki space) and a filing cabinet within the room (the wiki's pages).
Space and page permissions are granted on a whitelist basis i.e. the users you give permission to do certain actions are the only ones who are able to do those actions.
In order to access the drawers of the filing cabinet, the person needs the keys (space permissions) to the room (the space).
Let us take, for example, that the room is shared between two departments, Alpha and Bravo.
The keys to the room (space permissions) are provided to all staff of Alpha and Bravo.
Charlie and Delta, two other departments in the same company, cannot access the room, and therefore cannot access the drawers of the filing cabinet (the pages in the wiki space).
As Alpha and Bravo collaborate closely, most of the filing cabinet's drawers are not locked (no page permissions applied).
However, Alpha and Bravo need their own private section of the filing cabinets.
So, drawer A is locked, only accessible to Alpha staff (page viewing permissions for Alpha staff only).
Drawer B is also locked, only accessible to Bravo staff (page viewing permissions for Bravo staff only).
Page viewing and page editing permissions
The analogy above discussed permissions in a general sense. However, permissions are divided further into viewing and editing permissions.
- A user cannot edit a page he/she cannot view.
- Page viewing permissions are inherited by child (sub) pages i.e. all pages below the page on which the permission is applied
- Page edit permissions are not inherited by child pages.
- Wikis are for collaboration. You will find that people are reluctant to edit, even when they have permission to edit. Trust your collaborators, and remember you can always revert changes.
- Try not to restrict viewing and editing permissions on the same page as you may be unintended effects. Also, view and edit page permissions have different inherit schemes (refer to notes points 2 and 3) and will complicate matters.