+POSIX recommends that when specifying SA_RESETHAND, SA_NODEFER must
+also be specified.
+
+@item
+Support for SA_ONSTACK is missing on some platforms:
+mingw, MSVC 9, cygwin.
+
+@item
+Support for SA_SIGINFO is missing on some platforms:
+mingw, MSVC 9, Interix 3.5.
+
+@item
+Support for SIGCHLD, and thus for SA_NOCLDSTOP and SA_NOCLDWAIT, is
+missing on some platforms:
+mingw, MSVC 9.
+
+@item
+Support for SA_RESETHAND is missing on some platforms:
+NonStop.
+
+@item
+Support for SA_RESTART is missing on some platforms:
+mingw, MSVC 9, NonStop.
+
+@item
+In spite of having SA_SIGACTION, struct sigaction lacks the
+sa_sigaction member on some platforms:
+Irix 5.3.
+