Virtual custom property question

[David Bovill]

If I set the custom property of a control from somewhere else - lets  
say:

     set the display_Colour of group 1 to "red"

And this group has defined an appropriate setprop handler - say:

     setprop display_Colour someColour
         set the bgColor of btn 1 of me to someColour
     end display_Colour

Is there a way to find out which control is trying to set the custom  
property?