"dataready" accept filter?

Where can I read about "dataready" accept filter?

I did a google search and found FreeBSD references. I want
to read about 
it for NetBSD.

How is it used? Any man pages?

I am curious because I read that Apache httpd and BIND named
are affected 
by this. I wanted to know if this is specific to certain
operating 
systems.

  Jeremy C. Reed