base用来指定文件中所有链接相对URI的基准URI，也用于指定文件的基本目标框架名
base为head的子元素，必须置于head元素标签内容中，而且出现次数不能从多于一次
base应该放在任何包含相对URI的语句之前
link为空元素，在HTML中没有终止标签
属性
| 属性 | 属性值 | 说明 |
|---|---|---|
| ① href | URI | 指定用作文件中所有相对URI的基准的URI。此属性是必需属性 |
| ② target | 目标框架名 | 指定超链接打开的目标框架名，框架名可以在设置框架时指定。可能会用到的四个预定义名称：_parent表示超链接在上一级窗口中打开，_blank表示在新窗口中打开，_self表示在当前框架或窗口中打开，_top表示在浏览器整个窗口中打开，忽略任何框架 |
③ 通用属性：id、class、title、style、dir、lang、xml:lang  |
||
nbsp;
示范
1. 指定文件中所有相对URI的基准URI：
<base href="src/">
2. 指定链接的默认框架或窗口：
<base target="_top">
<base href="src/">
2. 指定链接的默认框架或窗口：
<base target="_top">
范例
下面的例子显示了XHTML文件基础结构：
运行
打印
下面的例子显示了XHTML文件基础结构：
运行打印
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>元素base</title>
<link href="default.css" rel="stylesheet" type="text/css">
<base href="http://www.yourdomain.com/" target="_blank">
</head>
<body>
此文档链接了外部样式表default.css <br>此文档使用了base元素，所有的相对链接都是相对base元素href属性指定的URI，超链接打开的目标窗口也是由base元素的target属性指定的<br>下面的超链接的URI为index.html，没有设定目标窗口，但是都由base元素指定了。<br>所以下面的图片也无法显示：<br><a href="index.html">Test the links</a><hr><img src="src/bugs.gif" alt="bugs bunny"><p>Authors may use the LINK element to provide a variety of information to search engines, including:</p>
<p>Links to alternate versions of a document, written in another human language. <br>
Links to alternate versions of a document, designed for different media, for instance a version especially suited for printing. <br>
Links to the starting page of a collection of documents. <br>
The examples below illustrate how language information, media types, and link types may be combined to improve document handling by search engines.</p>
<p>In the following example, we use the hreflang attribute to tell search engines where to find Dutch, Portuguese, and Arabic versions of a document. Note the use of the charset attribute for the Arabic manual. Note also the use of the lang attribute to indicate that the value of the title attribute for the LINK element designating the French manual is in French.<br>
</p>
</body>
</html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>元素base</title>
<link href="default.css" rel="stylesheet" type="text/css">
<base href="http://www.yourdomain.com/" target="_blank">
</head>
<body>
此文档链接了外部样式表default.css <br>此文档使用了base元素，所有的相对链接都是相对base元素href属性指定的URI，超链接打开的目标窗口也是由base元素的target属性指定的<br>下面的超链接的URI为index.html，没有设定目标窗口，但是都由base元素指定了。<br>所以下面的图片也无法显示：<br><a href="index.html">Test the links</a><hr><img src="src/bugs.gif" alt="bugs bunny"><p>Authors may use the LINK element to provide a variety of information to search engines, including:</p>
<p>Links to alternate versions of a document, written in another human language. <br>
Links to alternate versions of a document, designed for different media, for instance a version especially suited for printing. <br>
Links to the starting page of a collection of documents. <br>
The examples below illustrate how language information, media types, and link types may be combined to improve document handling by search engines.</p>
<p>In the following example, we use the hreflang attribute to tell search engines where to find Dutch, Portuguese, and Arabic versions of a document. Note the use of the charset attribute for the Arabic manual. Note also the use of the lang attribute to indicate that the value of the title attribute for the LINK element designating the French manual is in French.<br>
</p>
</body>
</html>
HTML文档中base元素后面所有的相对URI都受到base元素的href属性值的影响，超链接的目标窗口也可以由base元素的target属性设置。