public static int HitLayers { get; }

This value is automatically determined based on the layer of the PlatformerGameKit.HitTrigger prefab.

In the example scenes which use the default layers, this mask will simply include all layers. But when the UnityEngine.Physics2D collision matrix is properly configured the PlatformerGameKit.HitTrigger should be on a layer that only interacts with a few other layers so that hit queries don't waste performance considering objects that can't receive hits (such as platforms and other static parts of the environment).