Implementation same as Journal Items

In the standard OpenERP installation, if you click on Accounting --> Journal Entries sub menu ----> Journal Items, you see a tree view with two drop down at the top that allow you to filter by period and journal. I thought this was cool functionality, so I was looking into the source. The source of this view is:account.move.line.treeaccount.move.line My question is: how do they accomplish this functionality? I can't find the answers when looking at the source. To me, it just looks like a regular tree view. What tells the system to put the two dropdowns (and also provide filtering logic) at the top? Thanks, Tim