unitizerList ObjectJKExtraction process is a combination of steps:
Move Internal pointer with nextItem or prevItem
Retrieve item getItem
Check whether we're done iterating with done
done will return TRUE if the pointer is on either the
first or last entry depending on what direction you are iterating.
If you wish to iterate from the last item forward, you should either
reset with parameter reverse set to TRUE, or re-order
the items.
# S4 method for unitizerList
nextItem(x)a unitizerList object
unitizerList for getItem,
an item from the list, which could be anything