You will likely need to add more metadata than Popolo specifies.

It is recommended to reuse terms defined by the Dublin Core Metadata Initiative (DCMI), which publishes the most referenced linked open vocabularies, endorsed in IETF, ISO and ANSI/NISO standards. By reusing these terms, your terms are more likely to agree with those of others. If Popolo adds new metadata properties, it will reuse these terms.

DCMI Metadata Terms provides a complete list. DCMI also offers guides about creating and publishing metadata. Here are some sample terms and use cases:

The W3C Simple Knowledge Organization System also provides generic metadata terms, including: