An <iframe> that looks like it is a part of the containing document:
The seamless attribute is a boolean attribute.
When present, it specifies that the <iframe> should look like it is a part of the containing document (no borders or scrollbars).
|seamless||Not supported||Not supported||Not supported||Not supported||Not supported|
The seamless attribute is new in HTML5.
In XHTML, attribute minimization is forbidden, and the seamless attribute must be defined as <iframe seamless="seamless">.