A CDF may be placed in read-only mode via the Internal Interface using the <<SELECT_,CDF_READONLY_MODE_>> operation. Only read access will be allowed on the CDF --- all attempts to modify the CDF will fail. A CDF may be toggled in and out of read-only mode any number of times. (Note that attempts to modify a CDF may also fail if insufficient access privileges exist for the CDF --- the file system enforces this access.)