How is internal window trim/set installed?

[EmMi]

How is it usually done around windows?
Do you place the trim on top of/against the window frame, as the board symbolizes?
Or against the frame/wood that is further behind/at the side of the actual window frame?
In the picture, there are two windows that stand in a corner.

 

[EmMi]

Another picture from a different place, between two windows.
Same thing here, is the molding mounted on top of the frame or against the wood further back, beside the frame?
Of course, we must do the same everywhere, but maybe you can see more easily in this picture, it's most visible in the first one.

 

[Kurtivan]

Don't know if I understood correctly, but casings are mounted outside the frame or trim if you have it.