Image parallax?

Site URL: https://www.squarespace.com/sell-anything/time

I have a question about an effect on page on squaresapce.com 

This site https://www.squarespace.com/sell-anything/time has an image scroll parallax effect and I am wondering if this is a "built in" behaviour or did they create this with custom code? 

Thanks

That whole page is decked out to the max with customization's. I get it, it needs to not look like their base templates and I see a lot of features on those pages first and then drip-feed down to base templates/stock features. But yeah, that "sticky-parallax" effect is not a stock feature -- At least I don't think it is, which is too bad because if I could create websites that look halfway like their own pages, I'd have way more work 🙂

Do you know of anyone who is selling/making custom advanced parallax plugins for Squarespace?