”This is the theme to Garry’s show…,” went the opening bars of Shandling’s Showtime sitcom. When even the music is this self-obsessed, you’re in for something inventively meta. Playing himself, Shandling (and castmates) often interrupted the plots to talk to the camera and studio audience — a savvy gimmick that let the star toy with the format, and also redefined a tired genre. The copius EXTRAS in this complete-series set include six featurettes and commentaries with co-creator Alan Zweibel and former writers. If it all feels like a grand comedy master class, well, it is, and pay attention. A?