RDF.Description.triples

You're seeing just the function triples, go back to RDF.Description module for more information.
Link to this function

triples(description, opts \\ [])

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Specs

triples(t(), keyword()) :: [RDF.Star.Triple.t()]

The list of all triples within a RDF.Description.

When the optional :filter_star flag is set to true RDF-star triples with a triple as subject or object will be filtered. So, for a description with a triple as a subject you'll always get an empty list.