Predefined controls make it possible to implement commonly used Windows controls.
The AutoCAD PDB feature has a set of built-in, or predefined, tiles that can be used by themselves or as the basis for more complex tiles. Their definitions appear as comments within the base.dcl file.
When the user chooses an active tile—a button, for example—the dialog box responds by notifying the application controlling the dialog box. Any predefined active tile can have an associated action. The effect of an action can be visible to the user or can be purely internal (for example, a status update). Actions are accompanied by a reason code that indicates what triggered the action. The meaning of the reason depends on which kind of tile triggered it. The following tiles are selectable, active tiles: