alt
HTML alt Attribute （HTML alt属性）
The HTML alt attribute is used in HTML and XHTML documents. It specifies an alternative text which must be rendered if the element cannot be displayed for some reason. The alt attribute can also be used by screen readers to allow visually impaired users to interact with a webpage. To be accessible, an image must have an alt attribute. However, it may not contain text (empty or null attribute). （HTML alt属性用于HTML和XHTML文档。它指定了一个替代文本，如果由于某种原因无法显示元素，则必须呈现该文本。屏幕阅读器也可以使用alt属性，允许视障用户与网页进行交互。要访问，图像必须具有alt属性。但是，它不能包含文本（空或null属性）。）
You can use the alt attribute on the following elements: <area>, <img>, <input>.
It is required to use the alt attribute for the <img> element. For <input> elements, you can only use the alt attribute with <input type=“image”>.
Syntax
Syntax （语法）
<img alt="alternative text">
<area alt="alternative text">
Use the title attribute to create a tooltip for an image. （使用标题属性为图像创建工具提示。）
Example of the HTML alt attribute used on the <area> element:
<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
</head>
<body>
<p>Click on the logo or on one of the logo item to watch it closer:</p>
<img src="/uploads/media/news_gallery/0001/01/thumb_316_news_gallery_list.jpeg" width="250" height="150" alt="block" usemap="#blockmap">
<map name="blockmap">
<area shape="circle" coords="50,32,25" alt="html" href="/uploads/media/book_gallery/0001/01/d450f0358f947dffb3af91195c3002600d74101b.png">
<area shape="circle" coords="218,115,25" alt="css" href="/uploads/media/book_gallery/0001/01/25521e981b34da57c8f51baddc5b76351b855818.png">
<area shape="circle" coords="195,32,28" alt="php" href="/uploads/media/book_gallery/0001/01/4bbee6698c4884f25c46010d61b658dd62d2c04f.png">
<area class="homepage" shape="rect" coords="90,90,35,55" alt="php" href="https://www.w3cdoc.com/">
</map>
</body>
</html>
Example of the HTML alt attribute used on the <img> element:
<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
</head>
<body>
<img src="/uploads/media/default/0001/01/25acddb3da54207bc6beb5838f65f022feaa81d7.jpeg" alt="Aleq" width="200" height="185"/>
</body>
</html>
Example of the HTML alt attribute used on the <input> element:
<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
input {
（v.投资 ,投入）
vertical-align: middle;
（垂直居中对齐）
}
（。）
</style>
</head>
<body>
<form action="/form/submit">
Email:
（电子邮箱：）
<input type="email" name="Email">
<input type="image" src="https://i7.pngguru.com/preview/278/823/594/computer-icons-button-clip-art-green-submit-button-png.jpg" alt="Submit button" width="60" height="60">
</form>
</body>
</html>