VS represents it as "containment": a visual element "contains" its routine. Xcode (note spelling) represents it as "connection": a visual element is "connected to" its routine in another component.
I don't know if one or the other is more powerful, flexible, whatever. There's probably a certain amount of "X can be represent by Y" that goes in both directions, kind of like how any Turing-equivalent computer system can simulate any other Turing-equivalent system, it's only a question of representation.
I liken the "connection" metaphor to the rear panel of an A/V amplifier. It has lots of jacks, which you connect cables to, and the other end of the cable connects to another component. You can move connections without having to move the component itself, simply by unplugging the cable and plugging it into a different jack. For example, I can move the satellite video source to VID2 simply by moving the connecting cable. I don't have to physically move the satellite receiver box.
The "containment" metaphor is more like plugging cards into a computer motherboard, although technically that's really a bussed connection architecture.