Xfce 4.2 - How to set panel layer?

[Andrew Conkling]

Some time ago (probably on Mon, 22 Nov 2004 20:26:45 +0100)
Xan <DXpublica at telefonica.net> had occasion to say the following:
> 
> Mmmm.... I want that you reconsider it: I wonder if I could have
> taskbar bottom and panel up to taskbar. As in gnome I can do. See 
> http://img117.exs.cx/img117/2500/Captura-10.png

He does have a point.  In trying to recreate what he did in Gnome, I end
up with the taskbar being unusably hidden behind the panel.  What
happens when a user has both set to bottom?