Containing Flows in projections works similarly to Contain Flows in Rules. Contain Flows permits to filter out chosen flows. For more information on the uses of Contain Flows and its functioning see Contain Flows.
Contain Flows can be activated in a filter from the Filter Properties window, Contain Flows section. Contain Flows is defined for a given object type at a time and it can only be applied to types that have children defined as flows in Rules.
In the Contain Flows section, you see a list of flows to which filtering can be applied. You can activate the containment of a flow by unchecking its check-box. Remember to Save your modifications before exiting the Filter Properties window.