在查看此bootsnip时，我注意到HTML和CSS在<DOCTYPE> HTML标记之前已加载。因此，这使我想知道为什么作者要这么做。
作为参考，bootsnip的html代码的第一行是：
<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<!------ Include the above in your HEAD tag ---------->
<link href="//netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//netdna.bootstrapcdn.com/bootstrap/3.0.0/js/bootstrap.min.js"></script>
<script src="//code.jquery.com/jquery-1.11.1.min.js"></script>
<!------ Include the above in your HEAD tag ---------->
<!DOCTYPE html><html class=''>
<head><script src='//production-assets.codepen.io/assets/editor/live/console_runner-079c09a0e3b9ff743e39ee2d5637b9216b3545af0de366d4b9aad9dc87e26bfd.js'></script><script src='//production-assets.codepen.io/assets/editor/live/events_runner-73716630c22bbc8cff4bd0f07b135f00a0bdc5d14629260c3ec49e5606f98fdd.js'></script><script src='//production-assets.codepen.io/assets/editor/live/css_live_reload_init-2c0dc5167d60a5af3ee189d570b1835129687ea2a61bee3513dee3a50c115a77.js'></script><meta charset='UTF-8'><meta name="robots" content="noindex"><link rel="shortcut icon" type="image/x-icon" href="//production-assets.codepen.io/assets/favicon/favicon-8ea04875e70c4b0bb41da869e81236e54394d63638a1ef12fa558a4a835f1164.ico" /><link rel="mask-icon" type="" href="//production-assets.codepen.io/assets/favicon/logo-pin-f2d2b6d2c61838f7e76325261b7195c27224080bc099486ddd6dccb469b8e8e6.svg" color="#111" /><link rel="canonical" href="https://codepen.io/emilcarlsson/pen/ZOQZaV?limit=all&page=74&q=contact+" />
<link href='https://fonts.googleapis.com/css?family=Source+Sans+Pro:400,600,700,300' rel='stylesheet' type='text/css'>
你知道为什么会这样吗？