That's under Linux (not sure if that man page is maintained by glibc or the kernel seeing as it is a syscall).
That's pretty different under a system that cares : http://man.openbsd.org/OpenBSD-current/man2/write.2
That's pretty different under a system that cares : http://man.openbsd.org/OpenBSD-current/man2/write.2
They both describe all the parameters in the first sentence of the description.