Connect the desired Selection tag (point, polygon or edge) to this port.
The On input port takes a Boole value that enables (True) or disables (False) the node. The node is enabled automatically if you do not add this port.
Outputs the index numbers of the points, polygons or edges in the Selection tag one after the other. Edges are again a special case — for each edge, the node outputs the index numbers of its points.
Outputs the total number of elements in the Selection tag. In the case of edges, this value will actually be double the number of edges in the tag. This is because the node will output the number of points that make up the edges, not the actual number of edges.