How to use the domexception.SYNTAX_ERR function in domexception

}
        contentDoc.contentType = contentType.essence;
      }
    }

    const encoding = sniffHTMLEncoding(data, sniffOptions);
    contentDoc._encoding = encoding;

    const html = whatwgEncoding.decode(data, contentDoc._encoding);

    try {
      parseIntoDocument(html, contentDoc);
    } catch (error) {
      if (
        error.constructor.name === "DOMException" &&
        error.code === DOMException.SYNTAX_ERR &&
        contentDoc._parsingMode === "xml"
      ) {
        // As defined (https://html.spec.whatwg.org/#read-xml) parsing error in XML document may be reported inline by
        // mutating the document.
        const element = contentDoc.createElementNS("http://www.mozilla.org/newlayout/xml/parsererror.xml", "parsererror");
        element.textContent = error.message;

        while (contentDoc.childNodes.length > 0) {
          contentDoc.removeChild(contentDoc.lastChild);
        }
        contentDoc.appendChild(element);
      } else {
        throw error;
      }
    }