s + (previous ? '&' : '') + next;
    }

    // test shadowdom/custom elements polyfills together
    // preferring both if possible.
    let flags = [''];
    if (window.customElements) {
      // NOTE: disabled because Native ShadowDOM and Polyfilled CustomElements is not an expected use-case.
      // flags.push('wc-ce=true');
    }
    // if native is available, make sure to test polyfill
    if (Element.prototype.attachShadow && Node.prototype.getRootNode) {
      flags.push('wc-shadydom=true');
    }
