rd or cumulative hazard will be conditioned on survival up to
this time.   Predicted times returned with <code>"rmst"</code>, <code>"mean"</code>, <code>"median"</code> or <code>"quantile"</code>
will be times since time zero, not times since the <code>start</code> time.</p>
<p>A vector of the same length as <code>t</code> can be supplied to allow different
truncation times for each prediction time, though this doesn't make sense
in the usual case where this function is used to calculate a predicted
traject