Ask HN: What Technology does Optimizely use?

I was playing with Optimizely's experiment creator today and I really want to know how they grab any website and then allow the user to interact with it.

I want to do something similar, but instead of editing the code, I want to allow the user to select a region of the page and take a screenshot of it.

If someone can comment on how they do that, I would really appreciate it.