Hi Vandana, Modifiers are things like control-key, shift-key, alt-key, etc. Buttons you usually hold down and hit another key that performs the action. An action event happens because some component fires it. InputEvents happen because users have hit some key or mouse buttons. InputEvent should be used anytime you want to track key hit/release/type events or mouse clicks. In your little code snippet you are looking for mouse button 3 being clicked without any modifier keys being held down. This is probably because if a modifier was held down then another action would take place. Masking is used to let you figure out which mouse button or key was hit by the user. Regards, Manfred.