dateArithmetic({Root} and PopupCalendar

Hi guys, have a good days.

First of all, may I know that what is the actual function of dateArithmetic Root Container and PopupCalendar ?
My project is a Perspective Project.
It is possible to use the coding above to pass the start date and end date parameters to reporting module which I would like to generate a configurable report by using the start date and end date that the users insert.