+IRIX 5.3, OSF/1 4.0, Solaris 2.5.1, MSVC 9.
+@item
+This function does not support format directives that access arguments in an
+arbitrary order, such as @code{"%2$s"}, on some platforms:
+NetBSD 3.0, mingw, BeOS.
+@item
+This function does not return a byte count as specified in C99 on some
+platforms:
+HP-UX 11, IRIX 6.5, OSF/1 5.1, Solaris 9, mingw.