Compatibility View determines how Internet Explorer identifies itself to a web server and determines whether content is rendered ...

Compatibility View determines how Internet Explorer identifies itself to a web server and determines whether content is rendered in Quirks Mode or the Standards Mode available in the latest version of Internet Explorer.

If you enable this policy setting, Internet Explorer uses an Internet Explorer 7 user agent string (with an additional string appended). Additionally, webpages included in this list appear in Quirks Mode.