<!DOCTYPE html>
<html lang="zh-cn">
<head>
<meta charset="utf-8">
<title>表单元素[下]</title>
</head>
<body>
<form action="http://li.cc" novalidate oninput="res.value = num1.valueAsNumber * num2.valueAsNumber">
<!-- <select name="fruit" size="10" multiple>
<optgroup label="水果">
<option value="1">苹果</option>
<option value="2" selected>香蕉</option>
<option value="3">桔子</option>
</optgroup>
<optgroup label="粗粮">
<option value="4">小米</option>
<option value="5">大米</option>
<option value="6">玉米</option>
</optgroup>
</select> -->
<!-- <textarea name="content" rows="20" cols="40" wrap="hard">请留下您的建议！</textarea> -->
<!-- <input type="number" id="num1"> x <input type="number" id="num2"> =
<output for="num1 num2" name="res"> -->
<!-- <input type="text" required> -->
<!-- <input type="number" min="10" max="100"> -->
<input type="text" placeholder="请输入区号+座机" pattern="^[\d]{2,4}\-[\d]{6,8}$">
<button>提交</button>
</form>
</body>
</html>
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原文：http://onestopweb.iteye.com/blog/2230733