Controls whether a sheet can be viewed as a webpage. Usually you'd use the global variable SessionUser in its formula..
If the config's Code evaluates to a Blank or table/region where all cells are Blank then the sheet inherits its parent sheet's access permission. A 0x0 table, which is the default, falls under this case. If the sheet has no parent, then access is denied.
If the config's Code evaluates to a table/region where all cells are true, then access is granted.
Otherwise, access is denied, and an error code 403 is returned to the browser.