If you put an HTML comment above the doctype declaration, it causes IE7 to enter quirks mode, but not any other browsers.
<!-- This forces quirks mode in IE7 only --> <!doctype html> <html> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=Edge"> <title>Quirks mode in IE7!</title> </head> <body></body> </html>
Wow! That’s neat, I guess?
Why would anyone want to do this? Well, I had an application that required the IE6 box model for some pieces (so we could have 100% width input elements (with padding) inside dynamically sized table columns (with padding)). Forcing IE7 into quirks mode causes it to follow the IE6 box model, but I wanted to keep IE8+ in standards mode since you can use the
box-sizing CSS property to achieve the correct box model in more modern browsers.
So, you see, there’s at least one use case.