Understanding Bluez mgmt events

Hello,

I'm trying to understand the mgmt events in Bluez.
If I understand correctly, the MGMT_OP_... commands are first sent as following:

mgmt_send(adapter->mgmt, MGMT_OP_START_DISCOVERY, ...)

And then it should trigger a corresponding event like
MGMT_EV_DISCOVERING, MGMT_EV_DEVICE_FOUND etc.

I'm quite lost in understanding who, where and how generates these
MGMT_EV... events...
Could anybody please explain this on a simple example or showing a
piece of code in bluez sources where it is done...

Thanks in advance for any help,
Natalya