LibWeb: Don't mark mask-type as list-valued

Calme1709 · AtkinsSJ · commit 758432c1cd38 · 2025-12-02T12:14:27.000Z
This is distinct from the other `mask-*` properties and is not a
longhand of `mask`, and is thus not a coordinating value list longhand
diff --git a/Libraries/LibWeb/CSS/Properties.json b/Libraries/LibWeb/CSS/Properties.json
@@ -2799,7 +2799,7 @@
     "animation-type": "discrete",
     "inherited": false,
     "affects-layout": false,
-    "multiplicity": "coordinating-list",
+    "multiplicity": "single",
     "valid-types": [
       "mask-type"
     ],
diff --git a/Tests/LibWeb/Text/expected/css/typed-om-mask-type-not-list-valued.txt b/Tests/LibWeb/Text/expected/css/typed-om-mask-type-not-list-valued.txt
@@ -0,0 +1 @@
+PASS!
diff --git a/Tests/LibWeb/Text/input/css/typed-om-mask-type-not-list-valued.html b/Tests/LibWeb/Text/input/css/typed-om-mask-type-not-list-valued.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<div id="foo"></div>
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        try {
+            foo.attributeStyleMap.set("mask-type", new CSSKeywordValue("luminance"), new CSSKeywordValue("alpha"));
+            println("FAIL! Shouldn't allow setting multiple values for mask-type");
+        } catch {
+            println("PASS!");
+        }
+    });
+</script>
