+@item
+On some systems, @code{usleep} rejects attempts to sleep longer than 1
+second, as allowed by POSIX:
+mingw.
+@item
+This function is missing on some platforms. However, the replacement
+is designed to be lightweight, and may round to the nearest second;
+use @code{select} or @code{nanosleep} if better resolution is needed:
+IRIX 5.3, Solaris 2.4, older mingw, MSVC 9, BeOS.