Called to handle keyboard events when this snip has the keyboard focus and can handle events. The drawing context is provided, as well as the snip's location in display coordinates (the event uses display coordinates), and the snip's location in editor coordinates.
See also 'handles-events in get-flags.
The x and y arguments are the snip's location in display coordiantes. The editorx and editory arguments are the snip's location in editor coordinates. To get event's x location in snip coordinates, subtract x from (send event get-x).