writev(2) and IOV_MAX confusion

The is a big confusion over the correct definition of IOV_MAX in relation
to writev(2).  The man page for write(2)/writev(2) says you only have to
include <sys/uio.h> to get everything.  Unfortunatly IOV_MAX is not (no
longer?) defined there but in <sys/syslimits.h>.  Both Net- and OpenBSD
still define it in <sys/uio.h> but NetBSD only for compatibility.  For
them the correct place seems to be <sys/syslimits.h> too but only when
_XOPEN_SOURCE is defined.

What is the correct place for IOV_MAX?  And what has to be adjusted, the
man page or the .h files?

-- 
Andre