NoSwallow - bakkeby/dusk GitHub Wiki
If the Swallow functionality is enabled and a terminal window is marked with the Terminal flag, then any X window being started from the command line of that terminal will swallow the terminal. In simpler terms the new window will take the place of the terminal window.
The NoSwallow flag can be set via client rules to prevent specific X windows from
swallowing the terminal.
A typical example of this is running xev (Event Tester) in which a new window will being raised
but you still need to see the what the program is outputting to the terminal.