[css-color-5][editorial] Add examples of RCD alpha() serialization, w3c#13994

Author: svgeesus

css-color-5/Overview.bs

@@ -3643,6 +3643,23 @@ is the string "color(srgb 0 0 0.5)"
 
 </div>
 
+<div class="example" id="ex-serial-rcs-modern-alpha">
+For example, the serialization of the declared value of
+
+<pre class="lang-css">alpha(from red / 0.5)</pre>
+
+is the string "color(srgb 1 0 0 / 0.5)"
+because trailing zeros are trimmed,
+while the serialization of the declared value of
+
+<pre class="lang-css">alpha (from gold / calc(2/3))</pre>
+
+is the string "color(srgb 1 0.843137 0 / 0.666667)"
+because, by [[css-color-4#serializing-modern-alpha-values]]
+modern alpha values are serialized with six decimal places
+(unless there are trailing zeroes).
+</div>
+
 
 The serialization of the result of a relative color function
 depends on whether the keyword ''currentColor'' is the [=origin color=].