This function is generic; method functions can be written to handle
  specific classes of objects. Classes which already have methods for
  this function include lmList and lme.
random.effects is an alias for ranef; methods are
  implemented for the latter.
random.effects(object, ...)
ranef(object, ...)will depend on the method function used; see the appropriate documentation.
any fitted model object from which random effects estimates can be extracted.
some methods for this generic function require additional arguments.
Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S and S-PLUS", Springer, esp. pp. 100, 461.
ranef.lmList, ranef.lme