How does your generator port work?

I've seen on some trailers a shore power port on the front of the trailer for attaching a remote (portable) generator.



How does this work? How is it wired? Are the two inlets wired together, or are they each wired to a transfer switch?



I'm assuming if you are plugging a generator into it, the other shore power plug is not hot if you were to open it's door. Or is it?