Creator functions for the concomitant variable
  model. FLXPconstant specifies constant priors
  and FLXPmultinom multinomial logit models for the priors.
FLXPconstant()
FLXPmultinom(formula = ~1)Object of class FLXP. FLXPmultinom returns an
  object of class FLXPmultinom which extends class
FLXP directly and is used for method dispatching.
A formula for determining the model matrix of the concomitant variables.
Friedrich Leisch and Bettina Gruen
FLXPmultinom uses nnet.default from nnet to fit the
  multinomial logit model.