Function aggregation_dsl 

fn aggregation_dsl(
    model: &Model,
    func: FuncId,
    name: &str,
    args: &[Expr],
) -> Option<String>

AGG(args…) with its OVER clause after the first reduced argument (the parser accepts it after any), the window or WHERE there too. None when the shape has no spelling (a reduced argument that is not a plain reference, reduced arguments with different OVER lists, EXCEPT).