Details Section Question?

My Questions Is
How to let Detaisls Section fill empty space of the report
For example SalesInvoice Report

ReportHeader-->Sales Invoice Headers
ReprtFooter -->Sales Invoice Totals,etc
Now Details Section-->
i want it to fill the remain space with Salesinvoice Items even if it only contain few items

How do i do that?
Thanks in advancenot a issue man just put the item fields it will display the item it contain and will leave the remaining space blank automatically we don't have to do anything in that . This is the only benefits of using details section it will calculate paper size and then minus header and footer and remaining space will be used by details section

ok.