A selection set can consist of a single object, or it can be a more complex grouping: for example, the set of objects on a certain layer. A selection set is typically created by requesting a user to select an object in the drawing area before a command is started through pick first selection or at the

Select objects:

prompt when a command is active.

Selection sets are not persistent objects, if you need to maintain a selection set for use between multiple commands or future use, you will need to create a custom dictionary and record the object ids found in the selection set as a record.