code: def watchTextSelection(self, event=None):
          
          # Note that this isn't perfect - it is a key click behind when
          # selections are made via shift-arrow.  If this becomes important, it
          # can likely be fixed with after().
          if self.entry.selection_present(): # entry must be text entry type
              i1 = self.entry.index(SEL_FIRST)
              i2 = self.entry.index(SEL_LAST)
              if i1 >= 0 and i2 >= 0 and i2 > i1:
                  sel = self.entry.get()[i1:i2]
                  # Add to clipboard on platforms where necessary.
                  print('selected: "'+sel+'"')
docs: Callback used to see if there is a new text selection. In certain
          cases we manually add the text to the clipboard (though on most
          platforms the correct behavior happens automatically).