add_fit                 Add predicted values with standard errors to a
                        data.frame
constant                Keep a variable constant
mdl_to_ndat             Create a data.frame from a GAM object for
                        prediction
ndat_to_contour         Contour plot from a data.frame with
                        combinations of predictor values.
plot_contour            Contour plot from a GAM model object.
plot_curve              Curve plot of a partial effect from a GAM
                        model.
plot_partial            Plot a partial effect, dispatching by
                        view-variable types.
vary                    Varying values for prediction
