HTML 文档类型

所有 HTML 文档必须以 <!DOCTYPE> 声明开头。该声明并非一个 HTML 标签。它是一条“信息”，告知浏览器期望的文档类型。在 HTML5 中，<!DOCTYPE> 声明非常简单：

<!DOCTYPE html>

在更老的文档中（HTML 4 或 XHTML），该声明更为复杂，因为声明必须引用 DTD (Document Type Definition)。

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

不同 DOCTYPE 中的有效 HTML 元素

标签	HTML 5	HTML 4	XHTML
<a>	Yes	Yes	Yes
<abbr>	Yes	Yes	Yes
<acronym>	No	Yes	Yes
<address>	Yes	Yes	Yes
<applet>	No	Yes	No
<area>	Yes	Yes	No
<article>	Yes	No	No
<aside>	Yes	No	No
<audio>	Yes	No	No
<b>	Yes	Yes	Yes
<base>	Yes	Yes	Yes
<basefont>	No	Yes	No
<bdi>	Yes	No	No
<bdo>	Yes	Yes	No
<big>	No	Yes	Yes
<blockquote>	Yes	Yes	Yes
<body>	Yes	Yes	Yes
<br>	Yes	Yes	Yes
<button>	Yes	Yes	Yes
<canvas>	Yes	No	No
<caption>	Yes	Yes	Yes
<center>	No	Yes	No
<cite>	Yes	Yes	Yes
<code>	Yes	Yes	Yes
<col>	Yes	Yes	No
<colgroup>	Yes	Yes	No
<datalist>	Yes	No	No
<dd>	Yes	Yes	Yes
<del>	Yes	Yes	No
<details>	Yes	No	No
<dfn>	Yes	Yes	Yes
<dialog>	Yes	No	No
<dir>	No	Yes	No
<div>	Yes	Yes	Yes
<dl>	Yes	Yes	Yes
<dt>	Yes	Yes	Yes
<em>	Yes	Yes	Yes
<embed>	Yes	No	No
<fieldset>	Yes	Yes	Yes
<figcaption>	Yes	No	No
<figure>	Yes	No	No
<font>	No	Yes	No
<footer>	Yes	No	No
<form>	Yes	Yes	Yes
<frame>	No	No	No
<frameset>	No	Yes	No
<h1> to <h6>	Yes	Yes	Yes
<head>	Yes	Yes	Yes
<header>	Yes	No	No
<hr>	Yes	Yes	Yes
<html>	Yes	Yes	Yes
<i>	Yes	Yes	Yes
<iframe>	Yes	Yes	No
<img>	Yes	Yes	Yes
<input>	Yes	Yes	Yes
<ins>	Yes	Yes	No
<kbd>	Yes	Yes	Yes
<label>	Yes	Yes	Yes
<legend>	Yes	Yes	Yes
<li>	Yes	Yes	Yes
<link>	Yes	Yes	Yes
<main>	Yes	No	No
<map>	Yes	Yes	No
<mark>	Yes	No	No
<meta>	Yes	Yes	Yes
<meter>	Yes	No	No
<nav>	Yes	No	No
<noframes>	No	Yes	No
<noscript>	Yes	Yes	Yes
<object>	Yes	Yes	Yes
<ol>	Yes	Yes	Yes
<optgroup>	Yes	Yes	Yes
<option>	Yes	Yes	Yes
<output>	Yes	No	No
<p>	Yes	Yes	Yes
<param>	Yes	Yes	Yes
<pre>	Yes	Yes	Yes
<progress>	Yes	No	No
<q>	Yes	Yes	Yes
<rp>	Yes	No	No
<rt>	Yes	No	No
<ruby>	Yes	No	No
<s>	Yes	Yes	No
<samp>	Yes	Yes	Yes
<script>	Yes	Yes	Yes
<section>	Yes	No	No
<select>	Yes	Yes	Yes
<small>	Yes	Yes	Yes
<source>	Yes	No	No
<span>	Yes	Yes	Yes
<strike>	No	Yes	No
<strong>	Yes	Yes	Yes
<style>	Yes	Yes	Yes
<sub>	Yes	Yes	Yes
<summary>	Yes	No	No
<sup>	Yes	Yes	Yes
<table>	Yes	Yes	Yes
<tbody>	Yes	Yes	No
<td>	Yes	Yes	Yes
<textarea>	Yes	Yes	Yes
<tfoot>	Yes	Yes	No
<th>	Yes	Yes	Yes
<thead>	Yes	Yes	No
<time>	Yes	No	No
<title>	Yes	Yes	Yes
<tr>	Yes	Yes	Yes
<track>	Yes	No	No
<tt>	No	Yes	Yes
<u>	Yes	Yes	No
<ul>	Yes	Yes	Yes
<var>	Yes	Yes	Yes
<video>	Yes	No	No
<wbr>	Yes	No	No

HTML 文档类型

不同 DOCTYPE 中的有效 HTML 元素

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