Windows programming supports two types of windows: Modal and Modeless. The modal windows (DIALOGCREATE) are similar to a non-windows programming model where the application is in control. In midstream of processing you, as the programmer, decide to prompt the user for information (that is, READLIST). Processing is halted and other components of the application are inaccessible until the user supplies the requested information. For example, prompting the user for a file name to open a document is Modal.
When an application uses a modeless window (WINDOWCREATE), the user is in control. For example the commander in FMSLogo is modeless. The program is generally idle and reacts when the user triggers an event (such as pushing a button).
Modal windows should be avoided where possible because users prefer to be in control of their applications, rather than being forced to answer a question before the application will do anything else.
FMSLogo has some predefined modal dialog boxes that you can use in your Logo programs.