A quick update, due to some inaccurate bits in my previous reply:
RadPageLayout has two client (browser) feature sets: layout and responsive.
Layout feature set
Initially, we used css box-sizing to achieve layout parts, as it tends to be easier. However, box-sizing was not available on IE6 and IE7, so for 2014 Q2 release, we added extra wrappers just for IE7 to emulate the box-sizing.
As a result, all browsers that support prefix-free box-sizing
and IE7 will be able to use the current layout features.
Responsive feature set
The responsive feature set relies on prefix-free media queries. In terms, most browsers, IE7 and IE8 excluded, support the responsive feature set.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.