I'm sure it can be done a few ways. What I would like to see
is an enhancement to the Panel component,
like showContent="false/true" imgSrcUp="..." imgSrcDown="..."
By default showContent is false and the Panel works the way
it works now. If showContent="true" then the user can collapse the
panel content (the Title bar is still visible). The collapsing is
done by clicking on the image (arrow up/down. or plus/minus)
whatever the user wants. To be honest I'm surprised that something
like this doesn't exist yet as it's a very common user interface
component and very easy to do create in DHTML.