I've got an 8x10 plate holder made by Folmer Graflex that's got me flummoxed...

First of all, I'm confused as to how the plate is held in place. It doesn't seem to have any retaining clips at the top of the inset, as it does at the bottom...

Secondly, it does not fit into a standard 8x10 view camera. Is this holder specific to a Folmer plate camera?

Thirdly, since I can't use it, I'm going to need to sell it. What's it worth?

Any help greatly appreciated. I know, I know--- I'm a n00b.