+@item
+POSIX states that a setuid application can guarantee that fd 0 is
+open, but some systems guarantee this even for non-setuid programs.
+If an application is executed with fd 0 closed, use of @code{stdin}
+can affect an unrelated file that happened to be assigned to fd 0.
+The gnulib *-safer modules may be used to guarantee that fd 0 stays
+reserved for @code{stdin}.