Currently we have microdata on ecommerce product page, for things like description, price and other item level data. However, we'd like to also markup the individual variants.
Specifically, we sell shoes, so a product page will have a particular style on it, with multiple sizes for you to select from. Each size has it's on GTIN (barcode) and we'd like to add GTINx for each size. The sizes are in a select list, but I don't suppose the nature of the list matters, just the fact that I want to have multiple GTIN properties on the same page.
Any guidance on how best to mark it up to allow this?