Over the last year I have spent a good amount of time working with multiple WooCommerce powered websites. As the application becomes more complex, I am finding myself digging deeper into WooCommerce to find out how (or why) something works. I received a feature request that would require finding all orders for a product.
WordPress provides filters for sanitizing and authenticating your custom post meta. These filters have been around since 3.3 — and until now — were unknown to me. I happened to be reading Tadlock’s content-type-standards repository on Github and noticed some references to register_meta().