Topic on Template talk:Graph:Lines

Hello, I've read Vega doc and see it is possible to have tooltips. But couldn't put them on with . Could anyone work on that ?

 "signals": [{"name": "rightwidth", "expr": "width + padding.right", "init":"400"},
   {
     "name": "tooltip",
     "value": {},
     "on": [
       {"events": "group:mouseover", "update": "datum"},
       {"events": "group:mouseout",  "update": "{}"}

and

           "update": {
             "stroke": {"scale": "color", "field": "key"}, "x": {"scale": "xscale", "signal": "tooltip.category", "band": 0.5},
         "y": {"scale": "yscale", "signal": "tooltip.amount", "offset": -2},
         "text": {"signal": "tooltip.amount"},