When the ConnectionsZone control is rendered, it generates a UI based on the server controls on the page that are capable of forming connections. The ConnectionsZone control determines which server controls in the WebPartZoneBase zone on the page are providers, which are consumers, which connection points are available, and whether the server controls are currently connected or disconnected, and then it generates the UI accordingly.
Unlike most other Web Parts zones, a ConnectionsZone zone does not contain a unique type of server control associated with it. Instead, it serves a very limited purpose of providing a UI for users to connect or disconnect server controls that exist in some WebPartZoneBase zone on the page. The only controls contained in a ConnectionsZone control are the standard ASP.NET server controls that it generates as part of its UI for forming connections.