A report function that pre-computes the largest item in a group. The Items must be mutually comparable
among each other or the function will fail. Comparing dates with strings will not work.
Like all Total-Functions, this function produces a precomputed grand total. The function's result
is precomputed once and will not change later. Printing the result of this function in a group header
returns the same value as printed in the group-footer.
A group can be defined using the property "group". If the group property is not set, the function will process the
whole report.
author: Thomas Morgner
Return a completly separated copy of this function. The copy does no longer share any
changeable objects with the original function.
a copy of this function.