Should return true if this layer wants to handle input when it is the
active (top-most) layer. Returns false if any bound UserInterface should
not pass any input to the layer.
Called by the UI when the Layer above this one has been popped, making
this layer the top-most in the bound UserInterface. If a result value
was passed to UserInterface.pop, it is provided here as result.
If one is bound, the UserInterface will pass all bound input events to
this Layer if it is the active (top-most) layer. If this method returns
false (the default ), the respective lower-level input handler will be
called.
If this Layer is active (top-most) and accepting inputs, any keyboard
key down events not handled by the higher-level Layer.onInput handler
will be passed here by the bound UserInterface.