The physics engine supports three events:
EVENT_FRICTION, EVENT_IMPACT, and EVENT_ENTITY

EVENT_FRICTION (called for all involved PEs) sets both TARGET and NORMAL to collision point and its normal.
EVENT_ENTITY (moving PE/collider) and EVENT_IMPACT (receiver/collidee) only have TARGET set.

Please note that there was some change in this behavior and one of the flags was undefined, I do not remember which version number contains the complete implementation (it might be the Beta release).