VLAN Membership vs PVID

Hi all,

I'm new to managed switches, and just had a quick question...

If I'm setting up multiple VLANs, I'm wondering what the difference is between the VLAN Membership settings (where you click on the ports, per VLAN, and assign either tagged, untagged, or no traffic to).. and the PVID value you assign to each port on another screen (can't remember the screen right now, it's not in front of me).

I couldn't get other VLANs other than the default to work until I assigned VLAN IDs as the PVID to the ports I wanted those to be on.

I guess I'm a little confused, because I can assign untagged traffic to every port for every VLAN on the membership page, and then choose certain PVIDs for each port. When would I ever not have these two settings as a 1:1 match?

For example, VLAN 1's membership has untagged traffic on every port, but then only have PVID 1 set to ports 1-4.

Or the reverse, PVID set to 1 for every port, but the VLAN membership for 1 to only have untagged traffic on ports 1-4.

I hope I'm being clear, and that this makes sense.

Any clarification would be appreciated. 

(I tried searching for this before posting here)

Thanks.