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The objects placed in an APPLICATION or WINDOW structure are “controls.” “Control” is a standard Windows term used to refer to any screen object–command buttons, text entry fields, radio buttons, list boxes, etc. In most DOS programs, the term “field” is usually used to refer to these objects. In this document, the terms “control” and “field” are generally interchangeable.
Controls appear only in MENUBARs, TOOLBARs, or WINDOW structures. Controls are available to the user to select and/or edit the data they contain only when it has “input focus.” This occurs when the user uses the TAB key, the mouse, or an accelerator key combination to highlight the control.
A WINDOW also has “input focus” when it is the top WINDOW in the currently active execution thread. Since Clarion for Windows allows multi-threaded programs, the concept of which WINDOW currently has focus is important. Only the thread whose uppermost WINDOW has focus is active. The user may edit data in the WINDOW's control fields only when it has focus.