Updates the value.
        If the change exceeds the change delta observers and linked values are notified.

def value(self, new_value):
        """
        Updates the value.
        If the change exceeds the change delta observers and linked values are notified.  
        """
        datetime_value = None
        if new_value:
            datetime_value = new_value.strftime("%Y-%M-%dT%H:%M:%SZ")
        self._set_value(datetime_value)