Or maybe this way instead?

nixos/server/package-configs/forgejo/default.nix

@@ -70,15 +70,18 @@
         RENDER_COMMAND = ${pkgs.jupyter}/bin/jupyter nbconvert --stdout --to html --template full 
         IS_INPUT_FILE = true
         RENDER_CONTENT_MODE = no-sanitizer
-      ";
-      markup.sanitizer.juypter0 = "
+
+
+
+        ; the name after sanitizer doesn't really matter
+        [markup.sanitizer.jupyter0]
         ; Jupyter chiefly uses divs
         ELEMENT = div
         ; we will need access to html classes later
         ALLOW_ATTR = class
         ; we don't mind which classes we keep, so let's keep all of them
         REGEXP =
-    ";
+      ";
     };
   };