VMS Help FORTRAN, Statements, OPEN, USEROPEN  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  USEROPEN = p

  p  Is the symbolic name of the USEROPEN procedure.
     The USEROPEN parameter specifies a user-written
     EXTERNAL function that controls the opening of
     the file.

  The name must be declared EXTERNAL in the program unit with the
  OPEN statement, and if typed, it must be INTEGER*4.