A drawing set is a tree of attached drawings. Any of the attached drawings can have other drawings attached to them. The drawings that are not directly attached to the root of the drawing set (at level 0 of the tree) are called nested drawings.
You can use AcMapDrawingSet functions to edit and manipulate only drawings that are directly attached to the drawing set at the root level (level 0) of the drawing set. To access and edit drawings at deeper levels, use the functions of the AcMapAttachedDrawing class.
You can designate an attached drawing as active or inactive. When a query is executed in the project, only the active drawings are considered. When you work with object data in a project, open drawings instead of attaching them.
You can attach a reactor to a drawing set. A drawing set reactor notifies an application about drawing set-related events, such as attachment, detachment, activation, or deactivation. Whenever the drawing set is modified, an appropriate function of the reactor object is called before termination of the zero level Map transaction.