If the terminal application is not interested in mouse events and the display's scroll bar is not movable then send Up/Down key press events to the terminal instead.

This makes it possible to scroll up and down in 'less' and other applications using the mouse wheel. One key press is sent for every 5 degrees of mouse wheel rotation. Typical mouse wheels operate in steps of 15 degrees which equals 3 lines scrolled per notch. This default is the same as Vim's default mouse wheel scroll step.

As in gnome-terminal and others, this has side effects such as the mouse wheel scrolling through history results in the shell if the shell is run in a program such as screen.