openTab's semantics are the same as openWebsite's

(it's not a modifier for openWebsite, as I had previously though)

lib/Properties.hs

@@ -401,12 +401,6 @@ checkTileLayerProperty p@(Property name _value) = case name of
     "audioVolume" -> do
       isOrdInRange unwrapFloat 0 1 p
       requireProperty "playAudio"
-    "openWebsite" -> do
-      uselessEmptyLayer
-      suggestProperty $ Property "openWebsiteTrigger" (StrProp "onaction")
-      unwrapURI (Proxy @"website") p
-        (dependsOn . Link)
-        (const $ forbid "using openWebsite to access local html files is disallowed.")
     "openWebsiteTrigger" -> do
       isString p
       requireProperty "openWebsite"
@@ -416,9 +410,6 @@ checkTileLayerProperty p@(Property name _value) = case name of
     "openWebsiteTriggerMessage" -> do
       isString p
       requireProperty "openWebsiteTrigger"
-    "openTab" -> do
-      isString p
-      requireProperty "openWebsite"
     "url" -> complain "the property \"url\" defining embedded iframes must be \
                       \set on an object in an objectgroup layer."
     "exitUrl" -> do
@@ -480,6 +471,12 @@ checkTileLayerProperty p@(Property name _value) = case name of
                               , "openwebsitepolicy", "openwebsiteallowapi"
                               , "allowapi" ]
         -> forbidProperty name
+      | name `elem` [ "openWebsite", "openTab" ] -> do
+          uselessEmptyLayer
+          suggestProperty $ Property "openWebsiteTrigger" (StrProp "onaction")
+          unwrapURI (Proxy @"website") p
+            (dependsOn . Link)
+            (const $ forbid "accessing local html files is disallowed.")
       | otherwise ->
         warnUnknown p knownTileLayerProperites
     where