Question on Simple Binding

I have a toggle with a custom step having two values display and value . 

Then I have a chart below which shows line chart by country 

Now in my toggle I have Bar and Line  as display and hbar and line as values. I am trying to replicate the example from Einstein learning . 

I am doing a binding on the chart widget Visualization type property and "hbar" is replaced by below : 

 "visualizationType": "{{cell(Static_Step_1.selection, 0, \"Value\").asString()}}",

here "0" is hardcoded on the second parameter  , but when  i choose line or bar it automatically shows me the right chart , so  binding replace the selected value , but 0 on second  parameter refers to row 0 on static item right ? so how does it work for me . 

Also for testing I tried to replace the above expression with column instead of cell . 

{{column(static_1.selection, [\"value\"]).asObject()}}

but when i preview and select line it errrors out and i cannot go back to the dashboard. 

Any suggestions is appreciated.