How to use a material node data path as driver, that is located inside a material group? I would like to get the data path of a material node, that is located inside a material node group.
I would like to use it as a driver. In Blender 2.8 you can just copy a data path to use it for drivers e.g.

But if you do this for data inside a group, then it will be refreshed only at rendering time or if you play the animation, but not in realtime.

How to get the complete data value path for nodes inside of material groups?
How the complete data path have to be written?

node_tree.nodes["Group"]. what have to follow then to access a math node e.g.?
With blender 2.81 and up you can right-click in the field and choose "Copy as New Driver", then right click in the driven field and click "Paste Driver".



The resulting data path (in my file anyway) :