---
title: <msub>
slug: Web/MathML/Element/msub
translation_of: Web/MathML/Element/msub
---
<div>{{MathMLRef}}</div>

<p class="summary">MathML<code><strong>&lt;msub&gt;</strong></code>元素用来为表达式加下标，语法如下：<code><strong>&lt;msub&gt; base subscript &lt;/msub&gt;</strong></code>。</p>

<h2 id="属性">属性</h2>

<dl>
 <dt id="attr-class-id-style">class, id, style</dt>
 <dd>供<a href="/en-US/docs/CSS">样式表</a>使用。</dd>
 <dt id="attr-href">href</dt>
 <dd>用来设置标签点击后跳转的链接。</dd>
 <dt id="attr-mathbackground">mathbackground</dt>
 <dd>用来设置标签的背景色，可以使用<code><strong>#rgb</strong></code>、<strong><code>#rrggbb</code></strong>或者<a href="/zh-CN/docs/Web/CSS/color_value">HTML颜色名</a>。</dd>
 <dt id="attr-mathcolor">mathcolor</dt>
 <dd>用来设置标签文字的颜色，同样可以使用<code><strong>#rgb</strong></code>、<strong><code>#rrggbb</code></strong>或者<a href="/zh-CN/docs/Web/CSS/color_value">HTML颜色名</a>。</dd>
 <dt id="attr-subscriptshift">subscriptshift</dt>
 <dd>用来设置下标相对于表达式的基线的最小距离，它是一个<a href="/en-US/docs/MathML/Attributes/Values#Lengths">长度值</a>。</dd>
</dl>

<h2 id="例子">例子</h2>

<p>下述代码表示：<img alt="x1" src="/files/3202/msub.png" style="margin-left: 10px; vertical-align: middle;"></p>

<p>您的浏览器的渲染结果： <math> <msub> <mi>X</mi> <mn>1</mn> </msub> </math></p>

<pre class="brush: html">&lt;math&gt;

  &lt;msub&gt;
    &lt;mi&gt;X&lt;/mi&gt;
    &lt;mn&gt;1&lt;/mn&gt;
  &lt;/msub&gt;

&lt;/math&gt;
</pre>

<h2 id="规范">规范</h2>

<table class="standard-table">
 <thead>
  <tr>
   <th scope="col">Specification</th>
   <th scope="col">Status</th>
   <th scope="col">Comment</th>
  </tr>
 </thead>
 <tbody>
  <tr>
   <td>{{ SpecName('MathML3', 'chapter3.html#presm.msub', 'msub') }}</td>
   <td>{{ Spec2('MathML3') }}</td>
   <td>Current specification</td>
  </tr>
  <tr>
   <td>{{ SpecName('MathML2', 'chapter3.html#presm.msub', 'msub') }}</td>
   <td>{{ Spec2('MathML2') }}</td>
   <td>Initial specification</td>
  </tr>
 </tbody>
</table>

<h2 id="浏览器兼容性">浏览器兼容性</h2>

{{Compat("mathml.elements.msub")}}

<h2 id="关于Gecko的特殊说明">关于Gecko的特殊说明</h2>

<ul>
 <li>从Gecko 26.0 {{geckoRelease("26")}}开始，不允许使用&lt;none /&gt;作为子元素。The rendering has been made more consistent with equivalent configurations of {{MathMLElement("msup")}} and {{MathMLElement("mmultiscripts")}} and a bug with an incorrect application <code>of the </code><code>superscriptshift</code> attribute has been fixed (see {{bug("827713")}} for details).</li>
</ul>

<h2 id="相关链接">相关链接</h2>

<ul>
 <li>{{ MathMLElement("msup") }} (Superscript)</li>
 <li>{{ MathMLElement("msubsup") }} (Subscript-superscript pair)</li>
 <li>{{ MathMLElement("mmultiscripts") }} (Prescripts and tensor indices)</li>
</ul>