The positions, positionsNumeric, and positionsCalendar classes
are virtual classes that represent positions for series objects.
The timeInterval class represents time intervals.
The positionsNumeric class is a class union of
numericSequence and numeric, allowing representations of
numeric positions either by a sequence object or simply a vector.
The positionsCalendar is a VIRTUAL class and is
extended by timeDate and timeSequence.
The positions class is a class union of positionsNumeric
and positionsCalendar.
The timeInterval class is extended
by timeSpan and timeRelative.
timeDate class and timeSequence class.