Surprisingly I've stumbled upon a widget whose type was expression. I've never heard of such widgets before. According to LIST-QUERY-ATTRS it has the following attributes:
ROW,WIDTH-PIXELS,VALIDATE,X,Y,SENSITIVE,HEIGHT-PIXELS,TYPE,VISIBLE,MOVE-TO-BOTTOM,PRIVATE-DATA,SELECTABLE,SELECTED,MOVABLE,PARENT,RESIZABLE,MOVE-TO-TOP,HANDLE,NAME,NEXT-SIBLING,PREV-SIBLING,FRAME-X,FRAME-Y,BGCOLOR,FGCOLOR,HEIGHT-CHARS,WIDTH-CHARS,DYNAMIC,SIDE-LABEL-HANDLE,DCOLOR,LOAD-MOUSE-POINTER,MOUSE-POINTER,MANUAL-HIGHLIGHT,MENU-KEY,MENU-MOUSE,POPUP-MENU,HWND,HIDDEN,DATA-TYPE,TAB-STOP,TOOLTIP,CONTEXT-HELP-ID,DROP-TARGET,GET-DROPPED-FILE,END-FILE-DROP,NUM-DROPPED-FILES,INSTANTIATING-PROCEDURE,DBNAME,HELP,COLUMNS,FRAME-COL,FRAME-ROW,TABLE,INDEX,FRAME-NAME,FRAME,WINDOW,FONT
As I got in order to create such a widget you have to use FORM HEADER statement and all widgets which are normally fill-ins become expressions. The latter don't have any attribute to get their screen values though. That was quite an unexpected surprise. Moreover the attempt to query this attribute using CAN-QUERY leads to 4044 error. I hope I'm wrong about that. Does anybody know how to get their SCREEN-VALUEs?