Versioned.update

You're seeing just the function update, go back to Versioned module for more information.
Link to this function

update(changeset, opts \\ [])

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Specs

update(Ecto.Changeset.t(), keyword()) ::
  {:ok, Ecto.Schema.t()}
  | {:error, any()}
  | {:error, Ecto.Multi.name(), any(), %{required(Ecto.Multi.name()) => any()}}

Updates a changeset (of a versioned schema) using its primary key.

This function uses the Ecto.Repo module, first calling update/2 to update the record itself, and then insert/1 to add a copy of the new version to the versions table.