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在風格標籤內定義除了<header>下面的代碼的所有標籤可以被重新命名，爲什麼不能在html中重命名<header>標籤？
<!DOCTYPE html>
<html>
<head>
<style>
header {
background-color:black;
color:white;
text-align:center;
padding:5px;
}
nav {
line-height:30px;
background-color:#eeeeee;
height:300px;
width:100px;
float:left;
padding:5px;
}
section {
width:350px;
float:left;
padding:10px;
}
footer {
background-color:black;
color:white;
clear:both;
text-align:center;
padding:5px;
}
</style>
</head>
<body>
<header>
<h1>City Gallery</h1>
</header>
<nav>
London<br>
Paris<br>
Tokyo
</nav>
<section>
<h1>London</h1>
<p>London is the capital city of England. It is the most populous city in the United Kingdom, with a metropolitan area of over 13 million inhabitants.</p>
<p>Standing on the River Thames, London has been a major settlement for two millennia, its history going back to its founding by the Romans, who named it Londinium.</p>
</section>
<footer>
Copyright © W3Schools.com
</footer>
</body>
</html>
如果我重新命名，比如說，<nav>標籤<mytag>即使在當時的代碼將呈現與以前一樣。但是，如果我將<header>標記重命名爲<myheader>，那麼它不會呈現與以前相同的代碼。爲什麼如此？ <header>標籤有什麼特別之處？
我能想到的最好的例子。將