I came across the
property recently, and at first I did not understand why you would ever need it,
but today I actually used it and wanted to share my learnings with you!
In short, this property makes the entire document editable, as if you set
contentEditable on every tag in the page. Using this technique, you can
quickly adjust text on a webpage to make simple adjustments to your web app for
screenshots or demonstrations. You could even use this to quickly add or remove
text to test wrapping or responsive design with a variety of content.
document.designMode = "on"