If you have a pagestructure with a page in level 1, a page in level 2 and several subpages in level 3 and you want to give backend-access to the page in level 2 only, you will stumble apon a problem:
You can add the user or group in which the user is placed to the permissions-setting on the Level 1 page and choose Deny Access. This will inherit to the level 2 page and the level 3 pages. If you then change the permissions on the Level 2 page to Allow Access this too will inherit to the subpages. You will then need to change the permissions on each of these subpages individually.
In a case like this, it would be nice with a checkboks of some sort, like for instance: Inherit to Subpages. The default should probably be yes, but in the above mentioned example it would be great to deactivate the inheritance, so you don't have to change the permissions on each of the many subpages as well.
