F12 experiments can be activated from the Experiments tab which is the last tab along the navigation bar along the top of F12. After enabling an experiment you’ll need to close F12 and Microsoft Edge for the change to take effect.
As you make edits you will notice a dirty flag, an asterisk (*), in the document’s tab which implies that the document has changed but has not yet been saved.
Your edits can then be applied to the page by pressing the save icon or using the keyboard shortcut CTRL + S.
Once saved, you will be able to compare the modified document to the original document using the diff command.
Clicking the diff command will open up a new diff view of the document, highlighting any changes. Note that you will not be able to edit code in the **diff view*, but can do so by switching back to the original file on the tab bar.
All changes to the document will be lost when you navigate away or refresh from the current page.
You will not be able to edit when paused in the Debugger or when a document has been pretty printed.