This dialog opens when you pick nodes for velocity blending or sub-blending. If you click the Select Velocity Nodes button, the list displays only the objects being mixed in the current transition track. If you click the Select Sub-blend Nodes button, the list displays only the objects being mixed in the current transition track, except those objects that are already velocity blends.

To find an object in the list, enter the object's name and then press Enter.
Lists all the available objects.
Selects all objects in the list.
Selects no objects in the list.
Inverts the current list selection.
When on, the object hierarchy is shown by indenting. When off, all objects appear at the same level. Default=on.
When on, selecting an object selects that object's children. When off, only one object at a time is selected. Default=off.
This list shows the scene's named selection sets. Choosing a set from this list selects its members in the Node list.