>>> (indent 8)
        clip.onTransitionEnd
            .where((TransitionEvent e) => e.propertyName == 'height')
                .first.then((_) => clip.classes.add('expanded'));
<<<
        clip.onTransitionEnd
            .where((TransitionEvent e) => e.propertyName == 'height')
            .first
            .then((_) => clip.classes.add('expanded'));