Environmental Variables in HTML

There's At Least One

[inuwolf]

Before I got into PHP I remember remedying a CSS problem with the following little HTML trick which I found online:

<![if IE 6]>
<link rel="stylesheet" type="text/css" href="layout_ie.css" />
<![endif]>
<![if!IE 6]>
<link rel="stylesheet" type="text/css" href="layout.css" />
<![endif]>

Since that time I've learned--and loved--PHP and its environmental variables. I never knew HTML had them, but the script above convinces me environmental variables can be used outside of server-side languages, even if that's not what they're called. So here's my question:

Does HTML have any other variables like this one? What are they called? How do they work? As a server-side scripter recently returning to web design I find this very interesting.

[Robin_reala]

No - this is IE's conditional comments. They're proprietary to IE, but can be used in a useful way.

[inuwolf]

So I guess it's less a variable than a conditional statement that speaks to the browser. Are you sure it's proprietary to IE; that it can't speak to other browsers as well? Also, does HTML have anything else like this?