In reply to Todd.

The link discusses the iterative method by which generalized mixed models are fit.
"The generalized linear mixed model is approximated by a linear mixed model based on current values of the covariance parameter estimates. The resulting linear mixed model is then fit.... On convergence, new covariance parameters and fixed-effects estimates are obtained and the approximated linear mixed model is updated. Its parameters are again estimated iteratively."
These sentences show that at each iteration, the procedure fits an approximate linear mixed model.