Zone and Zone Type

Hi, all

I believe this question may be asked before, but I'm unable to find a clear answer.

When creating a custom zone, I need to specify a zone type (LAN and DMZ) - what is the difference between these two types?

Do these two type have anything to do with the LAN zone and DMZ zone?

Once a custom zone is created, how do I change to the type?

If I cannot change the zone type, is there anyway I can change zone without loosing all firewall rules and RED assigned to the zone?

In firewall rule, I can only specify Zone. When / where is the zone type actually used (apart from when creating custom zone)?

Thanks

Chung