           url: binary(),
           prev_url: binary() | nil,
           next_url: binary() | nil,
-          output: binary()
+          output: binary(),
+          extras: %{optional(binary()) => binary()}
         }
 
   @type maybe_tag :: Tag.t() | nil

    :url,
    :prev_url,
    :next_url,
    :output
  ]

  @spec generate(maybe_tag(), [map()], map()) :: Result.t([t()])

          title: list_title(tag, proj),
          posts: posts,
          url: Path.join([proj.base_url, list_dir, "page-#{page}.html"]),
          output: Path.join([proj.dest, list_dir, "page-#{page}.html"]),
          extras: %{}
        }
      end)

