Edit The Entire Webpage With Design Mode
Sometimes as a designer it is useful to just put your hands all over a website to tinker with it as you wish. With the HTML spec there is a property called designMode that when active, allows you to make the entire webpage editable.
You’ll see if you check this box you can then edit the contents of the page like it was a Google Doc or Microsoft Word document. Upon refresh the changes don’t persist. Allow users/designers to do this at their own risk!
Read more about it here