I'm trying to figure out how to use it.
I understand that this tag tell Google which page is the root parent / parent of the current page.
So, for example, on a page that's listing a product from a certain category, the
rel="index" value should be the product category page (the page which lists all products from that category). Am I right?
And the index value of that product category page is the "Products" page, ie. the page which lists products from all categories (or featured / most bought / popular products or whatever).
Is this how index should be used?
If yes, then what if the page which the index points to has
"noindex, follow", because it serves duplicate content?