docs: function(elem, listener) {
          var normalizedListener = function(e) {
              listener(normalizeWheelEvent(e));
          };
  
          EVENT_NAMES.forEach(function(name) {
              elem.addEventListener(name, normalizedListener);
          });
  
          return function() {
              EVENT_NAMES.forEach(function(name) {
                  elem.removeEventListener(name, normalizedListener);
              });
          };
  
      }