If the BY REFERENCE phrase is either specified or implied for a parameter,
the corresponding data item in the calling program occupies the same
storage area as the data item in the called program.
If the BY CONTENT phrase is specified or implied for a parameter, the
called program cannot change the value of this parameter as referenced in the CALL statement's USING phrase, though the called program can change the value of the data item referenced by the corresponding data-name in the called program's Procedure Division Division header. Changes to the parameter in the called program do not effect the corresponding argument in the calling program.