constructor(ytext, transaction, subs) {
    super(ytext, transaction);
    /**
     * Whether the children changed.
     * @type {Boolean}
     * @private
     */

    this.childListChanged = false;
    /**
     * Set of all changed attributes.
     * @type {Set<string>}
     */

    this.keysChanged = new Set();
    subs.forEach(sub => {
      if (sub === null) {
        this.childListChanged = true;
      } else {
        this.keysChanged.add(sub);
      }
    });
  }
Whether the children changed.
@type {Boolean}
@private