What I meant was that, iirc, in a an RA, there are broadcast flags called M and O which tell clients whether or not to use DHCPv6 and be governed by DHCP's IPv6 address assignments, rather than using the standalone procedures for making up an IPv6 address themselves.
I was talking about how the use of DHCPv6 is selected or not, not about how DHCP itself works. Does that make sense? Are we on the same page, or have I misunderstood?