+@item
+This header file is missing on some platforms that declare the
+@code{forkpty} and @code{openpty} functions in @code{util.h} or
+@code{libutil.h} instead: MacOS X 10.5, FreeBSD 6.0, NetBSD 5.0,
+OpenBSD 3.8.
+@item
+This header file is missing on some platforms:
+AIX 5.1, HP-UX 11, IRIX 6.5, Solaris 11 2010-11, BeOS.