[css-fonts-4] Seralize @ffv with last-defined, w3c#7964

Author: svgeesus

css-fonts-4/Overview.bs

@@ -7833,6 +7833,35 @@ Serializing font-related at-rules
 
 	</div>
 
+	Also,
+	following the principle of retaining only the last-defined value,
+	as well as the principle of shortest representation,
+	multiply-specified tuples and multiple blocks
+	are serialized as a single block
+	containing only the last-defined value.
+
+	<div class=example id="ex-serialize-same-font-feature-values
+">
+    For example, the declaration:
+
+	<pre highlight-css>
+		/* Repeated declaration names, and multiple blocks of the same type*/
+		@font-feature-values foo {
+			@swash { pretty: 0; cool: 2; }
+			@swash { pretty: 1; }
+		}
+	</pre>
+
+	would be serialized as:
+
+    <pre highlight=css>
+    /* Canonical serialization */
+    @font-feature-values foo {
+        @swash { cool: 2; pretty: 1; }
+    }
+    </pre>
+</div>
+
 
 <h2 id="platform-props-to-css" class="no-num">
 Appendix A: Mapping platform font properties to CSS properties</h2>