void outerHtmlHead(StringBuilder accum, int depth, Document.OutputSettings out) {
        if (accum.length() > 0 && out.prettyPrint()
                && (tag.formatAsBlock() || (parent() != null && parent().tag().formatAsBlock()) || out.outline()) )
            //换行并调整缩进
            indent(accum, depth, out);
        accum
                .append("<")
                .append(tagName());
        attributes.html(accum, out);

        if (childNodes.isEmpty() && tag.isSelfClosing())
            accum.append(" />");
        else
            accum.append(">");
    }