--expose and VIRTUAL_PORT redundancy?

[adamu]

Thanks for the great project.

What is the need for requiring the port to be exposed on the proxied container, besides good practice? My understanding is that exposing just adds metadata to the proxied container and does not affect the network, in the same way VIRTUAL_PORT also just metadata to the proxied container.

Why does the documentation state that the port must be exposed; is there a technical requirement?