buf.append(cause);
        if (cause instanceof SAXParseException) {
            final SAXParseException e = (SAXParseException) cause;
            if (e.getSystemId() != null) {
                buf.append(" at ").append(e.getSystemId());
            }
            final int lineNumber = e.getLineNumber();
            final int columnNumber = e.getColumnNumber();

     * @return the public ID, or null if not available
     */
    String getPublicId();

    /**
     * Returns the system ID of the XML
     * @return the system ID, or null if not available
     */
    String getSystemId();