FileStorageApi.File.upload_file_from_content

You're seeing just the function upload_file_from_content, go back to FileStorageApi.File module for more information.
Link to this function

upload_file_from_content(filename, container_name, content, blob_name)

Specs

upload_file_from_content(binary(), binary(), binary() | iodata(), binary()) ::
  {:ok, String.t()} | {:file_upload_error, map()}

This function will create a temporary file and upload to asset store