In regards to this rule: 9.1.3 some part of both feet of the server and the receiver shall remain in contact with the surface of the court in a stationary position from the start of the service (Law 9.2) until the service is delivered (Law 9.3); During the motion of serving, can I either a) lift the heel of one or both feet or b) if the heel is lifted, place it back down? So I'm essentially shifting my weight and changing my footprint on the floor, not taking a step or dragging my feet.