There are wireless setting which are not documented (yet).
Im was looking for the meaning of the values "vlan-id" and "vlan-mode". My first thought was the use of some experimental Q-in-Q-things for trunking VLANs via wireless bridges instead of creating vAPs for every VLAN.
But this doesn't make sense in context with "vlan-mode"...

What is it for? Is it for CAPsMan compatibility?

I believe these features are part of the wireless-fp so you can find the docs under the CAPsMAN page...

http://wiki.mikrotik.com/wiki/Manual:CAPsMAN

For your convenience I grabbed some interesting info for you from the page:
"vlan-id -- VLAN ID to assign to interface if vlan-mode enables use of VLAN tagging"
"vlan-mode -- VLAN tagging mode specifies if VLAN tag should be assigned to interface (causes all received data to get tagged with"