movement in crotch wood?

[TomFromStLouis]

It appears to me that his panel is proud of the frame on top while the frame is proud from below. This could be done by interlocking rabbetted pieces. Think of a grooved panel interlocking a grooved frame such that one lip of the panel is on top and one lip of the frame is proud along the underside. This is one way to float a panel without ever exposing a crack at the top to catch dust.

That's one way. The panel shown might not rattle in winter since he could glue the ends of his Koa board in place. But with a crotch piece that wants to move in all directions my approach would be to resaw the crotch and veneer some thin MDF or hardboard making a stable panel you can glue in all around. Very careful sizing would allow you to show the panel flush with the frame if you want; a proud panel like Gecko's might not be possible without heroic effort.

[MichaelMouse]

Can't really tell from the website pictures.

But if I had to guess I suspect that the lid frame has a groove that the panel rests inside.
The panel, in turn, also has a groove ... where the lower leg fits into the groove of the frame.
Think of 2 H's stacked inside each other.

I'll second that.  If not, that would work. 

The "feather" figure in a crotch has no particular direction to move.  Good sealing on such a small piece may be all you need.

[Gecko]

It is a floating panel.  Spot glued in the center of the short side. Grooves are cut a touch deep on both the frame and the panel to allow for expansion/contraction.

[Stwood_]

It is a floating panel.  Spot glued in the center of the short side. Grooves are cut a touch deep on both the frame and the panel to allow for expansion/contraction.

  Nice work

[jbmaine]

It is a floating panel.  Spot glued in the center of the short side. Grooves are cut a touch deep on both the frame and the panel to allow for expansion/contraction.

Thanks for all the info.
I hope you don't mind that I'm using box # 74 as a kind of template for mine. your work is truly inspirational.
 I only hope I can do it justice

                                     Jim