VMS Help PASCAL, Attributes, TRUNCATE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  The TRUNCATE attribute indicates that an actual  parameter  list
  for  a  routine can be truncated at the point that the attribute
  was specified.

  This attribute can be specified  on  a  formal  parameter  in  a
  routine declaration, and can be used with the PRESENT function.

  See the  "Compaq  Pascal  Language  Reference  Manual"  for  the
  complete description of using the TRUNCATE attribute.