code: function(setClosest, setObjectAssign, setCustomEvent) {
          closest      = setClosest      || closest;
          objectAssign = setObjectAssign || objectAssign;
          CustomEvent  = setCustomEvent  || CustomEvent;
      }
docs: Set shims
  @param {Function|null} [setClosest]
  @param {Function|null} [setObjectAssign]
  @param {Function|null} [setCustomEvent]