To add a little perspective, here is more info about what I'm trying to do.
On a page I want to have a drop down box that includes all the collections in my site. When the user selects a collection, I want to display all products & variants in the collection. My products are organized into smart collections. So, the product_type indicates the collection.
I would also be happy to see a way to get a list of products in a given collection.
Thanks!!