Global areas available to an MFS include system @-variables (@USERNAME, @ENVIRON_SET, etc.), user-defined global variables (@USER0-4), and labelled common areas.
A security MFS, for instance, might use the user name and privilege level variables to control access to files. A more sophisticated security system can establish a labelled common area at logon time. The labelled common area might contain lists of files and fields that the user has access to, to be examined by the MFS at every file operation.
