constructor(node, inertRoot) {
    /** @type {Node} */
    this._node = node;

    /** @type {boolean} */
    this._overrodeFocusMethod = false;

    /**
     * @type {Set<InertRoot>} The set of descendant inert roots.
     *    If and only if this set becomes empty, this node is no longer inert.
     */
    this._inertRoots = new Set([inertRoot]);

    /** @type {boolean} */
    this._destroyed = false;

    // Save any prior tabindex info and make this node untabbable
    this.ensureUntabbable();
  }
@param {Node} node A focusable element to be made inert.
@param {InertRoot} inertRoot The inert root element associated with this inert node.