Right-click a Periodic Condition node to add the
Destination Selection subnode and to change the selection for the destination. Depending on which COMSOL Multiphysics products your license includes,
Destination Selection subnodes are also available under other nodes such as
Cell Periodicity>Boundary Pair. This is the selection that COMSOL Multiphysics makes appear as the default selection in the
Selection list (as
Explicit 1, for example).