Here is an example I created interactively with a Continous factor and a Discrete Numeric factor.
levels = {1, 2, 3};
obj = DOE(
Custom Design,
{Add Response( Maximize, "Y", ., ., . ),
Add Factor( Continuous, -1, 1, "X1", 0 )}
);
Eval(
Substitute(
Expr( obj << Add Factor( Discrete Numeric, LLL, "X2", 0 ) ),
Expr( LLL ),
levels
)
);