-AIX 4.3.2, HP-UX 11, IRIX 6.5, Solaris 9, mingw, BeOS.
+AIX 4.3.2, HP-UX 11.23, IRIX 6.5, Solaris 9, mingw, BeOS.
+@item
+This function is not declared on some platforms:
+OSF/1 5.1.
+@item
+On some platforms, this function does not fail with @samp{EINVAL} when
+passed an empty string or a string containing @samp{=}:
+MacOS X 10.5, FreeBSD 6.0, NetBSD 1.6, OpenBSD 3.8, Cygwin 1.5.x.
+@item
+On some platforms, this function removes a leading @samp{=} from the
+value argument:
+Cygwin 1.5.x.