The schema.org official blog has announced support for enumerated lists. Adding this support allows developers using schema.org to use selected externally maintained vocabularies in their schema.org markup. According to the W3C-hosted schema.org WebSchemas wiki, “This is in addition to the existing extension mechanisms we support, and the general ability to include whatever markup you like in your pages. The focus here is on external vocabularies which can be thought of as ‘supported’ (or anticipated) in some sense by schema.org.”

In other words, “Schema.org markup uses links into well-known authority lists to clarify which particular instance of a schema.org type (eg. Country) is being mentioned.”

For example, consider a list of countries of the world. A developer could use this URI from Wikipedia to reference the USA or this one from the UN FAO, or this one from GeoNames.

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