Question about pong multiplayer tutorial

Hello, in multiplayer pong tutorial, this is indicated in parentheses:

("game")

Why is this done ?.

Is not it enough mouse.y?

From the Manual:

[quote:2rnzlpsa]If an individual layer has been scrolled, scaled or rotated, these expressions do not take that in to account - for that case, use the layer versions below.

mouse.X("layer")

mouse.Y("layer")

Return the position of the mouse cursor in game co-ordinates, with scrolling, scaling and rotation taken in to account for the given layer. The layer can be identified either by a string of its name or its zero-based index (e.g. Mouse.X(0)).

Ok clarified, thank you !.