Changes in HTML 5 - <iframe> Tag

What's new in HTML 5

The sandbox, seamless="seamless" and srcdoc attributes have been added.

Differences between HTML 5 and earlier versions of HTML

The 2000-2010 Recommendations from the W3C HTML Working Group defined the HTML namespace for the iframe element type name along with the names of all HTML element types. In older (pre-2000) versions of HTML, element type names were not associated with a namespace.