S3 and S4 methods for splitting "Intervals" or
  "Intervals_full" objects.
# S3 method for Intervals_virtual
split(x, f, drop = FALSE, ...)# S4 method for Intervals_virtual
split(x, f, drop = FALSE, ...)
A list of objects of the same class as x, split by the
  levels of f. Until R 2.15, special handling was not
  required. Subsequent changes to the base package
split function required an explicit method here, but
  code already provided by split.data.frame was
  sufficient.
"Intervals" or "Intervals_full" objects.
Passed to split.data.frame.
Passed to split.data.frame.
Passed to split.data.frame.