The parameter passing attributes indicate the passing  mechanism
  to be used for a parameter.

1  –  CLASS_A

  The CLASS_A attribute causes a formal parameter to be passed  by
  an  array  descriptor that describes contiguous arrays of atomic
  data types or contiguous arrays of fixed-length  strings.   This
  is  the  default  mechanism  for  conformant array parameters on
  OpenVMS VAX systems.  This attribute is illegal on parameters of
  schema types.

  See the "HP Pascal Language Reference Manual" for  the  complete
  description of using the CLASS_A attribute.

2  –  CLASS_NCA

  The CLASS_NCA attribute causes a formal parameter to  be  passed
  by  a noncontiguous array descriptor.  This attribute is illegal
  on parameters of schema types.  This is  the  default  mechanism
  for conformant array parameters on OpenVMS Alpha and OpenVMS I64
  systems.

3  –  CLASS_S

  The CLASS_S attribute causes a formal parameter to be passed  by
  a  single  descriptor  form  that  is  used  for scalar data and
  fixed-length strings.  This attribute allows routines written in
  VSI  Pascal  to  accept  actual  parameters  from languages that
  generate CLASS_S descriptors.

  See the "HP Pascal Language Reference Manual" for  the  complete
  description of using the CLASS_S attribute.

4  –  IMMEDIATE

  The IMMEDIATE attribute causes a formal  parameter  value  in  a
  routine declaration to be passed by immediate value.

  See the "HP Pascal Language Reference Manual" for  the  complete
  description of using the IMMEDIATE attribute.

5  –  REFERENCE

  The REFERENCE attribute causes the formal parameter in a routine
  to be passed by reference using foreign parameters.

  See the "HP Pascal Language Reference Manual" for  the  complete
  description of using the REFERENCE attribute.