<!DOCTYPE html> <html> <head> <script> function boom() { var frameRoot = document.getElementById("f").contentDocument.documentElement; var marquee = frameRoot.getElementsByTagName("marquee")[0]; marquee.__proto__ = []; frameRoot.appendChild(marquee); } </script> </head> <body onload="boom();"> <iframe id="f" src="data:application/xhtml+xml,<html xmlns='http://www.w3.org/1999/xhtml'><body><marquee></marquee></body></html>"></iframe> </body> </html>