Write an htmlHTML page with the following code. You will see that in the DOM selenium applies a webdriver attribute in the outerHTML:
<html> <head> <script type="text/javascript"> <!-- function showWindow(){ javascript:(alert(document.documentElement.outerHTML)); } //--> </script> </head> <body> <form> <input type="button" value="Show outerHTML" onclick="showWindow()"> </form> </body> </html>