For all of the coding challenges on the site, there is a "Start Over" button that wipes the coding environment and makes it as if you haven't done that challenge.

On the coding projects, that button does not exist, so you're not able to start over and see the criteria that needs to be met to complete the project. This button being added to the projects would be very helpful as sometimes I like to go back to past projects and re-do them as a refresher for the various skills they help you practice.