Requirements for doing a spin-off bsd branch?

[Loz]

* Sten Daniel Sørsdal <sten.daniel.sorsdal at wan.no> [2003-07-17 12:03]:
> 
> I am curious as to what is required (legally) to make a branch 
> of FreeBSD and call it somethingelseBSD?

the people at  http://www.dragonflybsd.org/  seem to be doing it.
Anyone know anything about it?

cheers,
/loz.