Help for SET JOINFLAGS:

SET JOINFLAGS allows a group to specify the flags assigned
to a user when they JOIN the group (if the group is open).

Note that this must be valid, else "+" will be set on joining
users. If no parameter is provided or the parameter is OFF, the
join flags will be returned to network default.

See "/msg &nick& HELP FLAGS" for details of the different flags that
are valid here.

Syntax: SET <!group>  JOINFLAGS [OFF|flags]

Examples:
    /msg &nick& SET !awesome-people JOINFLAGS OFF
    /msg &nick& SET !foo JOINFLAGS +
    /msg &nick& SET !foo JOINFLAGS +v
    /msg &nick& SET !foo JOINFLAGS +cfv
