[css-color-4] define predefined RGB space interconversion

Author: svgeesus

css-color-4/Overview.bs

@@ -3675,7 +3675,7 @@ Converting Lab to predefined color spaces</h4>
 
 	Conversion from one predefined RGB colorspace to another
 	requires multiple steps,
-	one of which is only used when the whitepoints differ.
+	one of which is only needed when the whitepoints differ.
 	To convert from <em>src</em> to <em>dest</em>:
 
 	<ol>
@@ -3689,6 +3689,9 @@ Converting Lab to predefined color spaces</h4>
 		<li>Convert from linear-light <em>dest</em>RGB to <em>dest</em>RGB (do gamma encoding)
 	</ol>
 
+	There is sample JavaScript code for this conversion
+	for the predefined RGB color spaces, in [[#color-conversion-code]].
+
 <h3 id="at-profile">
 Specifying a color profile: the ''@color-profile'' at-rule</h3>