CRS policer / shaper, how does burst work?

Hello,
When I follow CRS example and create 10M rate-limit, burst=100k is added automatically.

I think this does not make sense for 10Mbps rate-limit (100k < 10M).
Is burst absolute or relative?

How does burst relate to token bucket? Does token bucket have 3 limits (green, yellow, red)? How does burst control this?

How long is interface allowed to burst for?

http://wiki.mikrotik.com/wiki/Manual:CRS_features
If the packet exceeds the maximum rate or the burst size, which means no enough token for the packet, the packet is stored to buffer until there is enough token to transmit it

How large is buffer?
If packet is over rate-limit, I do not want to buffer (cause buffer-bload =o), how do I configure my CRS to just drop the packet?

Thanks!