Interface ModelMatrixOptions

A contrast per factor (default "contr.treatment"); a boolean variable takes it too. A name that is not a variable of the formula gives the warning variable 'B' is absent, its contrast will be ignored; a numeric variable (the response too) is an error.

The order of the levels of a factor ({ A: ["c", "a", "b"] }), as factor(x, levels = ...) in R.