*/
    public static String toString(final Document document) {
        assertArgumentNotNull("document", document);

        final StringBuilder buf = new StringBuilder(1000);
        appendElement(document.getDocumentElement(), buf);
        return new String(buf);
    }

    /**
     * {@link Element}を文字列に変換します。
     *
     * @param element
     *            要素。{@literal null}であってはいけません
     * @return 変換された文字列

        final XPath xPathApi = getXPathAPI().createXPath(f -> {});
        xPathApi.setNamespaceContext(new DefaultNamespaceContext(doc.getNodeType() == Node.DOCUMENT_NODE ? doc.getDocumentElement() : doc));
        return xPathApi.evaluateExpression(xpath, doc, XPathNodes.class);
    }

    protected XPathAPI getXPathAPI() {
        try {