RDF.IRI.default_base

You're seeing just the function default_base, go back to RDF.IRI module for more information.

The default base IRI to be used when reading a serialization and no base_iri option is provided.

The value can be set via the default_base_iri configuration. For example:

config :rdf,
  default_base_iri: "http://my_app.example/"

You can also set :default_base_iri to a module-function tuple {mod, fun} with a function which should be called to determine the default base IRI.

See section 5.1.4 of RFC 3987