Physics Builder Tools > Selections

Selections
A Selections () branch definition can either be an explicit selection or a selection being the result of a Boolean operation. Right-click the Definitions Library node to add this from the context menu.
Right-click 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 Selection Filter.
Named Selections in the COMSOL Multiphysics Reference Manual