What's this weird blue 8-long thin hinge piece?

Question

I've spent several hours on BrickLink now trying to identify this mystery piece. It doesn't have a part number on it, only the Lego logo. It looks kind of like a hinge or something that might snap into a doorway, but I haven't found anything similar. Can you help me?

It kind of looks like a window. Could you snap it in to a window holder? — Deadpool, Apr 15 '16 at 17:33
The hinge is to large for the snap holes in a standard-sized 4x3 window. It does snap with pieces like this, however. — Martin, Apr 15 '16 at 17:52
Pictures in focus! That is so amazing. Kudos to Martin for including high-res in-focus pictures. — chicks, Apr 17 '16 at 14:01