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.