+ If \code{age.max = NULL} (the default), it is assumed that
+ \code{age.min} gives exactly known ages. Otherwise, \code{age.max} and
+ \code{age.min} must be of the same length and give the intervals for
+ each node. Some node may be known exactly while the others are
+ known within some bounds: the values will be identical in both
+ arguments for the former (e.g., \code{age.min = c(10, 5), age.max =
+ c(10, 6), node = c(15, 18)} means that the age of node 15 is 10
+ units of time, and the age of node 18 is between 5 and 6).
+
+ The input tree may have multichotomies. If some internal branches are
+ of zero-length, they are collapsed (with a warning), and the returned
+ tree will have less nodes than the input one. The presence of
+ zero-lengthed terminal branches of results in an error since it makes
+ little sense to have zero-rate branches.
+