The URL of a formal, shared, and broadly applicable language for the digital resource.
Rationale: Consumers of digital resources spend far too much time trying and money to make sense of archaic formats that are poorly documented. Moreover, the lack of formal specifications mean that machines cannot readily process the content. With the exception of media languages (e.g. jpg), several languages (e.g. rdf, json-ld, json, xml) have now been standardized to allow structured content to be created, along with a syntax and semantics that makes them directly interpretable by people and machines. To satisfy this metric, the format of the digital resource must be represented by a BackusNaur Form (BNF) or variant thereof (e.g. EBNF, ABNF, etc), or be from one a registry of valid digital media formats or knowledge representation languages.