Setting tk_strictMotif to 1 causes Tk to, in some cases, produce a user interface more like the X Window System environment known as Motif and less like Tk.
Tk's xmfbox.tcl implements the file chooser dialog that is used when tk_strictMotif is set to 1.
Tk's text.tcl implements mouse-wheel scrolling only if tk_strictMotif is false. -- Ro