async _open(preventInitialFocus) {
      const prevented = !this.fireEvent("before-open", {}, true, false);
      if (prevented) {
        return;
      }
      if (this.isModal && !this.shouldHideBackdrop) {
        // create static area item ref for block layer
        this.getStaticAreaItemDomRef();
        this._blockLayerHidden = false;
        Popup_1.blockPageScrolling(this);
      }
      this._zIndex = (0, _PopupUtils.getNextZIndex)();
      this.style.zIndex = this._zIndex?.toString() || "";
      this._focusedElementBeforeOpen = (0, _PopupUtils.getFocusedElement)();
      this._show();
      this._addOpenedPopup();
      this.opened = true;
      this.open = true;
      await (0, _Render.renderFinished)();
      if (!this._disableInitialFocus && !preventInitialFocus) {
        await this.applyInitialFocus();
      }
      this.fireEvent("after-open", {}, false, false);
    }
Shows the block layer (for modal popups only) and sets the correct z-index for the purpose of popup stacking
@protected