seamless [HTML5 only]

This Boolean attribute indicates that the browser should render the inline frame in a way that makes it appear to be part of the containing document, for example by applying CSS styles that apply to the <iframe> to the contained document before styles specified in that document, and by opening links in the contained documents in the parent browsing context (unless another setting prevents this). In XHTML, attribute minimization is forbidden, and the seamless attribute must be defined as <iframe seamless="seamless">.