getME() provides a small, honest subset of the familiar lme4 extractor.
The fixed-effect design ("X"), random-effect design ("Z"), relative
covariance factor ("Lambda" / "Lambdat"), grouping factors ("flist"),
random coefficient names ("cnms"), response ("y"), fixed coefficients
("beta" / "fixef"), and theta vector ("theta") are rebuilt lazily
from the serialized R object.