/sys$common/syshlp/helplib.hlb FORTRAN, /STANDARD, SEMANTIC  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Controls whether the compiler produces informational messages for
  ANSI standard conforming statements that become nonstandard because
  of the way in which they are used.  Data type information and
  statement locations are considered when determining semantic
  extensions.

  Specifying SEMANTIC checking enables SYNTAX checking to be
  performed.