//define custom aggregate "all", now it can be used as column.summary.type
agg.all = function(arr, col){
return "Sum: " + format( agg.sum(arr, col) )
+", Max: " + format( agg.max(arr, col) )
+", Min: " + format( agg.min(arr, col) );
};
can you tell me the meaning of paramater arr and col?