final Document document) {
        // canonical
        final String canonicalUrl = getCanonicalUrl(responseData, document);
        if (canonicalUrl != null && !canonicalUrl.equalsIgnoreCase(responseData.getUrl()) && isValidUrl(canonicalUrl)
                && isValidCanonicalUrl(responseData.getUrl(), canonicalUrl)) {
            final Set<RequestData> childUrlSet = new HashSet<>();

     *     exception by calling [HttpUrl.parse]; it returns null for invalid URLs.
     */
    open fun url(url: String): Builder = url(canonicalUrl(url).toHttpUrl())

    // Silently replace web socket URLs with HTTP URLs.
    private fun canonicalUrl(url: String) =
      when {
        url.startsWith("ws:", ignoreCase = true) -> "http:${url.substring(3)}"