ing the dirty-checking strategy
       * for this element.  When true, Objects and Arrays will skip dirty
       * checking, otherwise strict equality checking will be used.
       */
      mutableData: Boolean
    },

    /**
     * Overrides `Polymer.PropertyEffects` to skip strict equality checking
     * for Objects and Arrays.
     *
     * Pulls the value to dirty check against from the `__dataTemp` cache
     * (rather than the normal `__data` cache) for Objects.  Since the temp
     * cache is clear