The Periodic Condition node can be used to define periodicity or antiperiodicity between two boundaries. The node can be activated on more than two boundaries, in which case the feature tries to identify two separate surfaces that can each consist of several connected boundaries. For more complex geometries, it might be necessary to add the Destination Selection subnode, which is available from the context menu (right-click the parent node) as well as from the Physics toolbar, Attributes menu.