A list containing three data.frames and three formula, one for each.
x data.frame containing the variables on the right-hand side
of the model formula.
y data.frame containing the variables on the left-hand side
of the model formula.
g data.frame containing the variables, if any, after
the conditioning bar | of the model formula.
x.formula formula containing the right-hand side
of the model formula.
y.formula formula containing the left-hand side
of the model formula.
g.formula formula containing the formula after the
conditioning bar | of the model formula.