The McRib is a barbecue sandwich that engineers the shape of ribs without any bones in it, and that act of imitation is the whole concept. A barbecue pork sandwich is normally pulled or chopped meat piled loose on a soft bun, the bun openly acknowledged as the least important part. The McRib instead presses ground and formed pork into a single flat slab molded with the ridged contour of a rib rack, so the build is a boneless patty wearing the silhouette of bone-in barbecue. The patty is the entire idea; everything else is arranged to sell the reference and hold it together.
The craft is in the patty and the sauce. The pork is formed into an even, cohesive rectangle with the molded ridges deliberately catching and holding sauce in their grooves, which is how a uniform processed patty is made to read as something pulled off a rib. It is lacquered heavily in a sweet, smoky, slightly tangy barbecue sauce, and the sauce is not a finish but the dominant flavor of the sandwich, doing the work that smoke and a long cook do in a true barbecue build. Slivered raw onion and dill pickle are the only other elements, and they are not garnish: they are the sharp, cold, acidic counter that keeps a uniformly sweet, saucy patty from collapsing into a single heavy register, exactly the structural job acid does in any sauced pork sandwich. The carrier is a long, soft, faintly chewy hoagie-style roll, sized to the slab and chosen to soak the sauce and give the hands a grip while the patty does all the talking, the same logic that makes a barbecue bun deliberately plain. The whole thing is assembled to a fixed pattern so the sauce, onion, and pickle land the same way every time.
The variations are a matter of dressing the same molded patty. A double stacks two slabs and doubles the sauce; regional sauce swaps push it sweeter or sharper; the wider field of American barbecue, pulled pork and brisket taken off real smoke, is the tradition it imitates and reads as its own subject entirely. Each of those deserves its own article rather than being crowded in here.