@on_trait_change( 'history:value' )
    def _value_changed ( self, value ):
        if not self._dont_update:
            history = self.history
            try:
                self._dont_update = True
                self.value        = history.value
                history.error     = False
            except:
                history.error = True

            do_later( self.set, _dont_update = False )

    #---------------------------------------------------------------------------
    #  Updates the editor when the object trait changes external to the editor:
    #---------------------------------------------------------------------------
Handles the history object's 'value' trait being changed.
dataset/ETHPy150Open enthought/traitsui/traitsui/wx/history_editor.py/_HistoryEditor._value_changed