When you define a dialog box as modal in AutoCAD VBA, the user must respond to the dialog box before any other part of the application is allowed to continue. No subsequent code is executed until the modal dialog box is closed through either the Hide or Unload method. This requires that you, as the developer of the application, think carefully about how and when you implement dialog boxes.
For example, you may have a dialog box that requires the user to select an object in the AutoCAD drawing. For the user to be able to pick the object from the AutoCAD Application window, you must hide the form by calling the Hide method. Once the object has been selected you use the Show method to redisplay the form, with all of its data still current, and continue with the application.