property token a chosen word
size system
The scale a product's categorical size values are expressed in (apparel-alpha, US footwear, EU footwear, ring, battery-IEC, mattress, …) — the meta facet that disambiguates a size token like '7' or 'M' into one comparable system. A chosen token read alongside size; grouped in the `facet` concern with it. (A later cleanup may make it a `qualified_by` of size, which is what it really is; co-grouped for now exactly as it was under the retired `variation` concern.)
Size system is answered with one word chosen from the size systems list — the same word shared across every product that uses it.
It belongs to facet — one facet of a product.