.
   *
   * Note, the performance characteristics of propagating large object graphs
   * will be worse by relying on `mutableData: true` as opposed to using
   * strict dirty checking with immutable patterns or Polymer's path notification
   * API.
   *
   * @polymerBehavior
   * @memberof Polymer
   * @summary Behavior to optionally skip strict dirty-checking for objects and
   *   arrays
   */
  Polymer.OptionalMutableDataBehavior = {

    properties: {
      /**
       * Instance-level flag for configur