In OSX Safari, how do I drag a single open window to an existing tab set?

Thanks, but I have multiple open tab sets and want to move a solo window to one of the windows with multiple tabs. It seems there must be a way to grab that solo and move it in with the tabs. My workaround is to add a tab to the solo window to create a tab that I can grab, but isn't there a "handle" for a solo window that is "grabbable"?

That discussion had multiple solutions that worked great. Thanks a lot!!