docs: function(target, eventType, callback) {
      if (target.addEventListener) {
        target.addEventListener(eventType, callback, false);
        return {
          remove: function() {
            target.removeEventListener(eventType, callback, false);
          }
        };
      } else if (target.attachEvent) {
        target.attachEvent('on' + eventType, callback);
        return {
          remove: function() {
            target.detachEvent('on' + eventType, callback);
          }
        };
      }
    }