Obtaining the coefficients and significance of net mobility effects in Diagonal Mobility Models using R's gnm() function

Question

How to obtain the net mobility effects in Diagonal Mobility Models (DMM)?

Suppose the model is specified using the gnm() function in R.

The baseline DRM model

gnm(formula = y ~ -1 + covariates + 
    Dref(origin, destination), data = data)

Now add the net mobility effects.

gnm(formula = y ~ -1 + covariates + 
    Dref(origin, destination, delta = ~1 + upward + downward), data = data)

The output does not specify the coefficients and significance of upward and downward, which are two binary indicators of upward and downward mobility. Then how to obtain them?

I checked the model outputs by summary(mod).

I checked the weight parameters by DrefWeights(mod)

But I did not see a direct output of the net mobility effects of the added terms.