os --- option source

        default range           syntax
           1,$       s[as | c | d | data | f | h | n | nr | nroff | p | r | s]
        
        This option sets other options for case, tabs, etc.
            as, s   -- assembler files   c          -- C files
            d, data -- data files        f          -- fortran files
            h       -- header files      n,nr,nroff -- nroff source files
            p       -- pascal files      r          -- ratfor files
        
        See the manual page for details.

        For general information about the options command, type "ho".