RFC4941 IPv6 privacy knobs and how to set them

Hello all.  Looking at some changes I made to configure my new gw router
last year but failed to document and check in, I find in my sysctl.conf:

+ # Use and prefer the RFC 4941 temporary addresses
+ net.inet6.ip6.use_tempaddr: 2
+ net.inet6.ip6.prefer_tempaddr: 2

Looking across the interwebs, I see information about setting these to 1,
and on using `ipv6_privacy` in /etc/rc.conf (which set them to 1), which
I did not do.

Is there documentation about what these variables mean, and if “2” is
a useful value different than “1”?  If so, how are they different?

Thanks.

        - Chris