QinQ and switchport dot1q-tunnel mode uplink command

Hi. Unfortunately, i didn't find the info about the switchport dot1q-tunnel mode uplink command in the manual.
What did the "uplink" mode? 

On example... I have a simple setup on the SW1:

SW1 interface ethernet 1/1
...
 switchport allowed vlan add 1101 untagged
 switchport native vlan 1101
 switchport dot1q-tunnel mode access

And the some other switch that connected to this (SW1 ethernet 1/1) port is trunk port with only tagged frames.

SW1 interface ethernet 1/2
...
switchport allowed vlan add 1101 tagged
switchport mode trunk

In this case, i'm getting the double-tagged (Some C-tags and S-VLAN 1101) frames at SW1 interface ethernet 1/2 OUTPUT, and that's what i want (like in cisco). I'm NOT using the " switchport dot1q-tunnel mode uplink" command on the SW1 interface ethernet 1/2, and everything is fine. So... My question is: what did the " switchport dot1q-tunnel mode uplink" command?