Previously, you could only redirect a domain to the site’s primary domain. Now, when toggling on a domain redirect, a textbox will be prepopulated with the primary domain and you can edit it to redirect to any domain you like.
That’s Basic mode. If you switch to Advanced mode, you can define the complete URL it redirects to as well as the HTTP redirect status code it should use. You can even use Nginx variables in the URL it redirects to.
Managing a site’s domains has been moved out of the Settings tab to a new Domains tab for easier access and a bit more room.