Examples:

Assume that M1,...,Mn are multiplicative models and A1,...,An are additive models.

XSPEC> model A1              ! The single component A1 is the model

XSPEC> model A1 A2           ! model = A1 + A2

XSPEC> model ,,,M1           ! model = (A1+A2)*M1

XSPEC> model M2/             ! model = M2*[A2*M1]

XSPEC> model ,,,,a1          ! model = M2*[A2*M1]+A1

XSPEC> model a1,a1,m1        ! model = (A1+A1)*M1   Note that though
                                  first and second components are the
                                  same form, their parameters are varied
                                  separately.

XSPEC> mo A1,null,A2,M1      ! model = A1 + [A2*M1]

XSPEC> mo M1(A1+M2(A2))      ! model = M1*[A1+M2*A2]

XSPEC> mo ,,,,,B1/b          ! model is as above but with B1 included as
                                  a background model.