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my $viewbutton = $mw->Button(-text=>"Change view", -command=>\&changeV
+iew);

...
    updateGraph();
    return;
}

The only events for which bindings may be specified are those related 
+to the mouse and keyboard (such as Enter, Leave, 
ButtonPress, Motion, and KeyPress) or virtual events. The handling of 
+events in canvases uses the current item defined
...
events are directed to the current item, if any. Keyboard-related even
+ts are directed to the focus item, if any (see 
the focus method below for more on this). If a virtual event is used i
+n a binding, that binding can trigger only if 
the virtual event is defined by an underlying mouse-related or keyboar
+d-related event.