public static void appendChildren(final NodeList children, final StringBuilder buf) {
        assertArgumentNotNull("children", children);
        assertArgumentNotNull("buf", buf);

        final int length = children.getLength();
        for (int i = 0; i < length; ++i) {
            appendNode(children.item(i), buf);
        }
    }

    /**
     * {@link NamedNodeMap}の文字列表現を追加します。
     *
     * @param attrs