VMS Help PASCAL, Declaration Section, Routine Declaration, formal_parameter_list, undiscriminated_schema_name  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The name of an undiscriminated  schema  type.   If  you  have  a
  user-defined,  formal  parameter  of  an  undiscriminated schema
  type, the corresponding actual parameter must  be  discriminated
  from the same schema type as that of the formal parameter.

  When you pass a string expression to a formal,  value  parameter
  of  type  STRING, the actual parameter's current length (not its
  declared maximum length) becomes both the maximum length and the
  current length of the formal parameter.