UPDATE: Preview Layout

Previews the first layout with the given name for the current store page.

Page.aspx?PreviewLayoutName=MyLayout

This is what allows us to do get creative with existing pages. Such as building product ‘quick views’ from the category page, basically a full product page layout with as much or as little power as you need.
It’s an alternate skin/layout on the product page itself and referenced in the URL by name.