Less commonly used but very useful tags under Xhtml_HTML/Xhtml_Web page production

Xhtml has many uncommon but useful tags. Some can get twice the result with half the effort, some can improve semantics, and some can improve ease of use. I have summarized some of them. The principle of summary is that it is useful and usable, that is, most browsers must support it, otherwise it will not count as "highlighting". "Yes. What's the use of just sighing at the "lot"?
tag
Function: The tag specifies the default link address or link target for all links on the page. Sometimes we need to make all the links on the homepage open in a new window. We usually write the links like this, but using this tag can do it at once!
Attributes:
Href: link address
target: target. Its value can be _blank, _parent, _self, _top. It can be used in other than Strict mode. This usage is what I use First discovered on 163.com.
Usage:

<code class="html"><span class="tag"><head</span><span class="tag">></span><!&mdash;写在head标签之间--<span class="tag">> <br><span class="tag"><base</span><span class="aname"> href</span>=<span class="avalue">"http://www.qq.com/"</span> <span class="tag">/></span> <!&mdash;将默认链接定义为http://www.qq.com/--<span class="tag">> <br><span class="tag"><base</span><span class="aname"> target</span>=<span class="avalue">"_blank"</span> <span class="tag">/></span> <!&mdash;将默认链接目标定义为新窗口中打开--<span class="tag">> <br><span class="tag"></head></span></code><p><br><font size="4"><strong><caption>标签</strong></font><br>    <strong>作用：</strong>caption标签用来定义表格的标题，给表格定义一个标题，来说明这个表格是干什么的，岂不是很有“语义”，caption应该写在table之后，默认的样式是居中显示在表格的顶部。你可以通过css来改变它的样式。<br>    <strong>用法：</strong><br></p>

<code class="html"><span class="tag"><table</span><span class="aname"> width</span>=<span class="avalue">"200"</span><span class="aname"> border</span>=<span class="avalue">"1"</span> <span class="tag">></span> <br><span class="tag"><caption</span><span class="tag">></span> <span class="mlcom"><!--caption应该写在table之后--></span> <br>其实我是caption <br><span class="tag"></caption></span> <br><span class="tag"><tr</span><span class="tag">></span> <br><span class="tag"><td</span><span class="tag">></span><span class="entity"> </span><span class="tag"></td></span> <br><span class="tag"><td</span><span class="tag">></span><span class="entity"> </span><span class="tag"></td></span> <br><span class="tag"></tr></span> <br><span class="tag"><tr</span><span class="tag">></span> <br><span class="tag"><td</span><span class="tag">></span><span class="entity"> </span><span class="tag"></td></span> <br><span class="tag"><td</span><span class="tag">></span><span class="entity"> </span><span class="tag"></td></span> <br><span class="tag"></tr></span> <br><span class="tag"></table></span></code><p><br><font size="4"><strong><thead>标签、<tbody>标签、<tfoot>标签</strong></font><br>    作用：thead、tfoot 
以及 
tbody标签跟他们的名字那样，分别是表格的头部（很多人只是用th）、主题、和底部，他们能让表格更加语义化的同时，也能让我们更加方便的控制表格的表现。国外还有人用很变态地方法用这三个表其做出标题能跟随表格，或者tbody固定高度，多出的行数出现滚动条。有兴趣的可以搜素下或者是这做一下。<br>注意：<font color="#ff0000">如果您使用 thead、tfoot 以及 tbody 
元素，您就必须使用全部的元素。它们的出现次序是：thead、tfoot、tbody，这样浏览器就可以在收到所有数据前呈现页脚了。</font><br>    <strong>用法：</strong><br></p>

<code class="html"><span class="tag"><table</span><span class="aname"> border</span>=<span class="avalue">"1"</span><span class="tag">></span> <br><span class="tag"><thead</span><span class="tag">></span> <br><span class="tag"><tr</span><span class="tag">></span> <br><span class="tag"><th</span><span class="tag">></span>科目<span class="tag"></th></span> <br><span class="tag"><th</span><span class="tag">></span>分数<span class="tag"></th></span> <br><span class="tag"></tr></span> <br><span class="tag"></thead></span> <br><span class="tag"><tfoot</span><span class="tag">></span> <br><span class="tag"><tr</span><span class="tag">></span> <br><span class="tag"><td</span><span class="tag">></span>总分<span class="tag"></td></span> <br><span class="tag"><td</span><span class="tag">></span>159<span class="tag"></td></span> <br><span class="tag"></tr></span> <br><span class="tag"></tfoot></span> <br> <br><span class="tag"><tbody</span><span class="tag">></span> <br><span class="tag"><tr</span><span class="tag">></span> <br><span class="tag"><td</span><span class="tag">></span>语文<span class="tag"></td></span> <br><span class="tag"><td</span><span class="tag">></span>99<span class="tag"></td></span> <br><span class="tag"></tr></span> <br><span class="tag"><tr</span><span class="tag">></span> <br><span class="tag"><td</span><span class="tag">></span>数学<span class="tag"></td></span> <br><span class="tag"><td</span><span class="tag">></span>60<span class="tag"></td></span> <br><span class="tag"></tr></span> <br><span class="tag"></tbody></span> <br><span class="tag"></table></span></code><p><br><font size="4"><strong><fieldset>标签和<legend>标签</strong></font><br>    <strong>作用：</strong><fieldset>元素用来分类表单中的元素，而<legend>则能给这个组定义一个标题。你一定见过类似下面domo的布局吧！他们也可以通过css定义样式。<br>    <strong>用法:</strong><br></p>

<code class="html"><span class="tag"><form</span><span class="tag">></span> <br><span class="tag"><fieldset</span><span class="tag">></span> <br><span class="tag"><legend</span><span class="tag">></span>基本信息<span class="tag"></legend></span> <br>姓名: <span class="tag"><input</span><span class="aname"> type</span>=<span class="avalue">"text"</span> <span class="tag">/></span> <br>性别: <span class="tag"><input</span><span class="aname"> type</span>=<span class="avalue">"text"</span> <span class="tag">/></span> <br><span class="tag"></fieldset></span> <br><span class="tag"></form></span></code><p><br><font size="4"><strong><sub> 标签和<sup> 标签</strong></font><br>    作用：<sub> 
标签和<sub> 
标签分别是上标和下标，虽然他们在各个浏览器的表现不一样，你<br>同样可以使用css定义他们的样式。<br>    <strong>用法：</strong><br></p>

<code class="html">2<span class="tag"><sup</span><span class="tag">></span>我是上标<span class="tag"></sup></span> <br>2<span class="tag"><sub</span><span class="tag">></span>我是下标<span class="tag"></sub></span></code><p><br><font size="4"><strong><label>标签</strong></font><br>    <strong>作用：</strong>label 
标签的使用可以扩大表单的点击区域来改进表单的易用性。看看下面的用法：点击文字的时候相当于点击了单选控件，这样用户体验是不是会更好一些？<br>    <strong>用法：</strong><br></p>

<code class="html"><span class="tag"><form</span><span class="tag">></span> <br><span class="tag"><label</span><span class="aname"> for</span>=<span class="avalue">"nan"</span><span class="tag">></span>先生<span class="tag"></label></span> <br><span class="tag"><input</span><span class="aname"> type</span>=<span class="avalue">"radio"</span><span class="aname"> name</span>=<span class="avalue">"sex"</span><span class="aname"> id</span>=<span class="avalue">"nan"</span> <span class="tag">/></span> <br><span class="tag"><br</span> <span class="tag">/></span> <br><span class="tag"><label</span><span class="aname"> for</span>=<span class="avalue">"nv"</span><span class="tag">></span>女士<span class="tag"></label></span> <br><span class="tag"><input</span><span class="aname"> type</span>=<span class="avalue">"radio"</span><span class="aname"> name</span>=<span class="avalue">"sex"</span><span class="aname"> id</span>=<span class="avalue">"nv"</span> <span class="tag">/></span> <br><span class="tag"></form></span></code><br><font size="4"><strong><optgroup> 标签</strong></font><br>    <strong>作用：</strong><option></option> 
标签可以给select中的option进行分组，这在下拉项目很多的时候很有用，配合label标签给每组命名。你也可以像淘宝那样给每组用css定义不同的颜色。<br>    <strong>用法：</strong><br>

<code class="html"><span class="tag"><select</span><span class="tag">></span> <br><span class="tag"><optgroup</span><span class="aname"> label</span>=<span class="avalue">"自驾游"</span><span class="tag">></span> <span class="mlcom"><!--配合label标签给每组命名--></span> <br><span class="tag"><option</span><span class="tag">></span>省内<span class="tag"></option></span> <br><span class="tag"><option</span><span class="tag">></span>省外<span class="tag"></option></span> <br><span class="tag"></optgroup></span> <br><span class="tag"><optgroup</span><span class="aname"> label</span>=<span class="avalue">"旅行社"</span><span class="tag">></span> <br><span class="tag"><option</span><span class="tag">></span>省内<span class="tag"></option></span> <br><span class="tag"><option</span><span class="tag">></span>省外<span class="tag"></option></span> <br><span class="tag"><option</span><span class="tag">></span>国外<span class="tag"></option></span> <br><span class="tag"></optgroup></span> <br><span class="tag"></select></span></code><br>    你如果对更多的xhtml标签感兴趣，可以考虑看一看《HTML和XHTML权威指南》这本书，你也能在网上找到电子版的。我看过英文影印版的，虽然是英文但也不是太难看懂。<br>    你要是知道其他很有用的标签告诉我们吧！