Is it possible to create an HTML quine?
It's certainly not possible with "plain" HTML. Obviously it would be possible to do with JavaScript, but it's also possible with CSS:
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>This is the title</title>
<style type="text/css"><![CDATA[
* {
display:inline;
white-space:pre;
}
html:last-child {
white-space:normal;
}
html:before {content:'<html xmlns="http://www.w3.org/1999/xhtml">';}
html:after {content:'</html>';}
head:before {content:'<head>';}
head:after {content:'</head>';}
title:before {content:'<title>';}
title:after {content:'</title>';}
style:before {content:'<style type="text/css"><![CDATA[';}
style:after {content:']]\00003e</style>';}
body:before {content:'<body/>';position:absolute;left:0;}
]]></style>
</head>
<body/>
</html>