Hi,

there are at least three different ways to recognize the widget which invoked a callback. One of them, attaching unique 
user data to each widget, you already named - and that is often the best way.

Of course you could also compare the 'widget' pointer directly, as in:
   if ( widget == ABW_widget1 ) {
      /* do widget1 processing */
   }
   else if ( widget == ABW_widget2 ) {
      /* do widget2 processing */
   }
   else {
      /* do something else? */
   }

But then it's much nicer to go by the 'widget name' (which is actually an index):

   switch ( ApName( widget ) ) {
   case ABN_widget1:
      /* do widget1 processing */
   case ABN_widget2:
      /* do widget2 processing */
   default:
      /* do something else? */
    }

- Thomas