@item
POSIX does not require this variable to be declared, and it is indeed not
declared on some platforms:
-MacOS X 10.5, FreeBSD 6.0, NetBSD 3.0, OpenBSD 3.8, IRIX 6.5, Solaris 10.
+MacOS X 10.5, FreeBSD 6.0, NetBSD 5.0, OpenBSD 3.8, IRIX 6.5, Solaris 11 2010-11.
@item
On MacOS X 10, this variable is not declared. Up to MacOS X 10.4, one can use
@smallexample