Allow to copy sounds for custom JS with ObjectProperty `loadSound`

lib/Properties.hs

@@ -309,7 +309,7 @@ checkObjectProperty p@(Property name _) = do
         when (null (objectName obj) || objectName obj == Just mempty) $
           complain $ "Objects with the property "<>prettyprint name<>" set must \
                      \be named."
-    | name `elem` [ "openSound", "closeSound", "bellSound" ] -> do
+    | name `elem` [ "openSound", "closeSound", "bellSound", "loadSound" ] -> do
         isString p
         unwrapURI (Proxy @"audio") p
           (dependsOn . Link)