RDF.Graph.delete_descriptions

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

delete_descriptions(graph, subjects)

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Specs

delete_descriptions(
  t(),
  RDF.Statement.coercible_subject() | [RDF.Statement.coercible_subject()]
) :: t()

Deletes all statements with the given subjects.

If subjects contains subjects that are not in graph, they're simply ignored.