[CentOS] RADVD and default IPv6 gateway

the man page for RADVD says:

       radvd is the router advertisement daemon for IPv6. It listens to 
router
       solicitations and sends router advertisements as described in 
"Neighbor
       Discovery  for  IP Version 6 (IPv6)" (RFC 2461).  With these 
advertise-
       ments hosts can automatically configure their addresses and some  
other
       parameters. They also can choose a default router based on these 
adver-
       tisements.


But there is nothing I see in man radvd.conf that answers how hosts 
choose a default router, nor can I find anything else about this.

Anyone know the answer or where to get the information???