Selections
The Selections () branch definition under the Definitions Library can either be an explicit selection or a selection being the result of a Boolean operation.
Right-click Selections to add Selection, Selection Filter Sequence, and Extra Dimension Selection subnodes. There are also other features available as subnodes to the Selection Filter Sequence: Override Rule Filter, Selection Component Filter, and Multiphysics Coupling Filter.
Creating Named Selections in the COMSOL Multiphysics Reference Manual