mls cos extend

I was doing some reading on the commands "switchport priority extend cos x"  and "mls qos cos x"

Cisco documentation says "If you configure the mls qos cos 3 command on a port, it sets the CoS value of all the frames from the PC to 3 and does not alter the frames from the phone"

"The switchport priority extend cos 0 configures the IP phone to change the CoS value to 0."

so with a typical PC to phone setup does:

"switchport priority extend cos 2"

-or-

"mls qos cos 2"

-with-

"mls qos trust cos"

both set the PC cos value to 2 and while trusting the phone tags?