This tab controls who sees a document and what they are able to do to it. There are several different levels of access for each document.
The access control tab
No Access— the document cannot be seen by anyone other than the document author.
Visible— the document can be seen but not edited by selected entities.
Simple Editing— the document can be edited but not deleted by selected entities.
Advanced Editing— the document can be edited and components can be added or deleted by selected entities. The entire document can also be deleted.
All Visitors— the document can be seen by all visitors to the site.
All Registered Users— the document can only be seen by registered users of the site.
Individual Users— the document can only be seen by selected individuals.
Groups— the document can be seen by all members of a particular group.