POV-Ray : Documentation : Restrict Write but Allow Read
  POV-Ray 3.6 Documentation Online View No Restrictions Restrict Read/Write Restrict Write but Allow Read

If this option is chosen. POV scripts can read anything, but file creation and file write is only allowed in the specified directories (see Low-Level Configuration for more information on how to specify which directories).

Another way to put it is that I/O Restrictions are turned off for reading files, but not for writing them. No Restrictions Restrict Read/Write

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