checked
HTML checked Attribute （HTML选中属性）
The HTML checked attribute is a boolean attribute and specifies that an <input> element must be checked when the page loads.
You can use this attribute only on the <input> element (<input type=“checkbox”> and <input type=“radio”>).
It is also possible to set the checked attribute after the page loads, with JavaScript. （也可以在页面加载后使用JavaScript设置checked属性。）
Syntax
Syntax （语法）
<input type="checkbox|radio" checked>
Example of the HTML checked attribute:
<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
</head>
<body>
<h2>HTML Form Example</h2>
<form action="/form/submit" method="post">
<input type="radio" name="game" value="football" checked> Football
<input type="radio" name="game" value="basketball"> Basketball
</form>
</body>
</html>