How does transition time work?

Configuration
1

Anyone knows how transition time for light works?
I have some Philips Hue bulbs integrated via Zigbee2mqtt and I use transition time in HA. This works fine but I wonder how this works.
When I look at mqtt traffic I see no telegrams indicating something about fadetime etc. I only see the final level.

2

It is a command sent to the light once. The light then takes care of the transition. This is why not all lights support transitions and transitions cant be interrupted.

3

Okay I see but shouldn´t there be some part of the MQTT telegram telling the light what transition time is used?