plot is the method for plotting irregular time-series objects.
All series are displayed on a single set of axes, by default using different
colours, linetypes, and widths. If the vectors defining these attributes are
short, they are cycled. lab and leg are alternatives for labelling
the curves - these are located using function labcurve() from package
Hmisc on CRAN.
print is the method for printing irregular time-series objects.
The format for the dates is determined at the time the 'its' object is created.