As you can see, the inner foundation has bra cups, boning, a waist stay, and grommets for a corset lacing. As there's no lacing in the grommets yet, I'm guessing it has to be put in once she's in the dress. I'm also guessing she had plenty of help getting dressed. The zipper is metal, which would be required to stand up to the strain of the corset lacing. No invisible zippers here!
The outside of the dress is gorgeous, too. (Though I'll admit the inside gets me more excited.) Here she is with the designer (and my secret crush), Zac Posen.
You can see that there's horsehair braid in the hem to support the folds. The seaming at the bottom calls to mind Charles James's own Clover Gown, which I believe to be his masterpiece.
Of course, the more exciting news here is that the Met is exhibiting James's work. And there's a reproduction of the Clover gown--complete with robotic arms! (Read the fascinating article on the technology here.) I am beyond impatient to get to see this exhibit, and of course I will report back on it here.