Showing IPv4 and IPv6 multicast group membership on Linux

The traditional way of listing multicast group memberships on any Unix system is with the netstat(1) command. But on Linux, the ip(1) tool can show both IPv4 and IPv6 groups in a single command:

# ip maddr show
1:    lo
    inet  224.0.0.1
    inet6 ff02::1
    inet6 ff01::1
74:    eth0.2
    link  01:00:5e:00:00:01
    link  33:33:00:00:00:01
    inet  224.0.0.18
    inet  224.0.0.1
    inet6 ff02::1:ff04:4253
    inet6 ff02::1
    inet6 ff01::1