@item
This header file is not self-contained --- it requires @code{<string.h>}
before @code{FD_ZERO} can be used --- on some platforms:
-AIX 7.1, Solaris 11 2010-11.
+AIX 7.1, Solaris 11 2011-11.
@end itemize
Portability problems not fixed by Gnulib: