L7 : OPTIONAL argument keyword usage
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Optional arguments passed to a routine shall have their keyword specified.

To be avoided : 

.. code-block:: fortran
   :caption: OPTIONAL argument keyword

   !! interface of OPT_ARG subroutine is below
   CALL OPT_ARG( IVAL1,IVAL2,IVAL3)


   SUBROUTINE OPT_ARG( ARG1, ARG2, ARG3)
   
   INTEGER(KIND=JPIM), INTENT(IN)          :: ARG1
   INTEGER(KIND=JPIM), INTENT(OUT)         :: ARG2
   INTEGER(KIND=JPIM), INTENT(IN),OPTIONAL :: ARG3