How should I mask when spraying trim?
My first question is why are you planning on spraying trim in a completed house? (windows, door trim, base boards, crowns) I could understand maybe spraying out trim in new construction before the  finished floors are installed and walls are not painted yet. You are going to have to cover everything including the furniture! Every edge is going to have to be taped and all hardware has to come off or get masked The second item that comes to mind is that you will have to use a bunch of Flowtrol to shoot a semi-gloss paint thru a 211 tip. You may also want to back brush to get an even finish and avoid "orange peel".  I really think it would be faster and easier to use a good Purdy sash brush and paint your trim the old fashion way, one stroke at a time.