The size set of the product. Size set is an identification table for the size. Ex: "38" is a womens' euro shoe size, but value "38" set out of context could indicate any kind of size. Size sets should be used and ideally describe the kind of product and what intended target group the size is meant for, or at least help to categorize the size value so it can be easily distinguished from other size values in your product data feed.
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