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diff --git a/testing/web-platform/tests/css/geometry/DOMMatrix-attributes.html b/testing/web-platform/tests/css/geometry/DOMMatrix-attributes.html
new file mode 100644
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+++ b/testing/web-platform/tests/css/geometry/DOMMatrix-attributes.html
@@ -0,0 +1,66 @@
+<!DOCTYPE html>
+<title>Geometry Interfaces: DOMMatrix attributes</title>
+<link rel="help" href="https://drafts.fxtf.org/geometry/#dommatrix-attributes">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+const initial = {
+    a: 1, b: 0, c: 0, d: 1, e: 0, f: 0,
+    m11: 1, m12: 0, m13: 0, m14: 0,
+    m21: 0, m22: 1, m23: 0, m24: 0,
+    m31: 0, m32: 0, m33: 1, m34: 0,
+    m41: 0, m42: 0, m43: 0, m44: 1,
+};
+
+// Attributes that always preserve is2D.
+["a", "b", "c", "d", "e", "f",
+ "m11", "m12", "m21", "m22", "m41", "m42" ].forEach(attribute => {
+    test(() => {
+        let m = new DOMMatrix();
+        assert_true(m.is2D);
+        assert_equals(m[attribute], initial[attribute]);
+        m[attribute] = 42;
+        assert_true(m.is2D);
+        assert_equals(m[attribute], 42);
+    }, `DOMMatrix.${attribute}`);
+});
+
+// Attributes that clear is2D for values other than 0 or -0.
+["m13", "m14", "m23", "m24", "m31", "m32", "m34", "m43" ].forEach(attribute => {
+    test(() => {
+        let m = new DOMMatrix();
+        assert_true(m.is2D);
+        assert_equals(m[attribute], initial[attribute]);
+        m[attribute] = 0;
+        assert_true(m.is2D, "0 preserves is2D");
+        assert_equals(m[attribute], 0);
+        m[attribute] = -0;
+        assert_true(m.is2D, "-0 preserves is2D");
+        assert_equals(m[attribute], -0);
+        m[attribute] = 42;
+        assert_false(m.is2D, "a value other than 0 or -0 clears is2D");
+        assert_equals(m[attribute], 42);
+        m[attribute] = 0;
+        assert_false(m.is2D, "is2D can never be set to true after having been set to false");
+        assert_equals(m[attribute], 0);
+    }, `DOMMatrix.${attribute}`);
+});
+
+// Attributes that clear is2D for values other than 1.
+["m33", "m44" ].forEach(attribute => {
+    test(() => {
+        let m = new DOMMatrix();
+        assert_true(m.is2D);
+        assert_equals(m[attribute], initial[attribute]);
+        m[attribute] = 1;
+        assert_true(m.is2D, "1 preserves is2D");
+        assert_equals(m[attribute], 1);
+        m[attribute] = 42;
+        assert_false(m.is2D, "a value other than 1 clears is2D");
+        assert_equals(m[attribute], 42);
+        m[attribute] = 1;
+        assert_false(m.is2D, "is2D can never be set to true after having been set to false");
+        assert_equals(m[attribute], 1);
+    }, `DOMMatrix.${attribute}`);
+});
+</script>