methods for them:  length,
  length<-,
  dimnames,
  dimnames<-,
  dim,
  dim<-,
  names,
  names<-,
  levels<-,
  as.character,
  as.complex,
  as.double,
  as.integer,
  as.logical,
  as.raw,
  as.vector,
  is.array,
  is.matrix,
  is.na,
  is.nan,
  is.numeric,
  rep,
  seq.int
  (which dispatches methods for "seq")
  and xtfrm
  In addition, is.name is a synonym for is.symbol and
  dispatches methods for the latter.
Note that all of the group generic functions are also internal/primitive and allow methods to be written for them.
  .S3PrimitiveGenerics is a character vector listing the
  primitives which are internal generic and not group generic.
  Currently as.vector, cbind,
  rbind and unlist are the internal
  non-primitive functions which are internally generic.
  For efficiency, internal dispatch only occurs on objects, that
  is those for which is.object returns true.
methods for the methods which are available.