A container for “subgraphs” - node networks which exist inside the Box and can be exposed by promoting selected internal plugs onto the outside of the Box.
Boxes can be used as an organisational tool for simplifying large graphs by collapsing them into sections which perform distinct tasks. They are also used for authoring files to be used with the Reference node.
Container for user-defined plugs. Nodes should never make their own plugs here, so users are free to do as they wish.