[css-color-4][editorial] Historical reasons

Author: svgeesus

css-color-4/Overview.bs

@@ -2127,7 +2127,8 @@ HSL Colors: ''hsl()'' and ''hsla()'' functions</h2>
 	while ''100%'' or ''100'' is white and ''0%''  or ''0'' is black.
 
 	<!-- https://github.com/w3c/csswg-drafts/issues/9222 -->
-	If the saturation is less than ''0%''
+	For historical reasons,
+	if the saturation is less than ''0%''
 	it is clamped to ''0%''
 	at parsed-value time,
 	before being converted to an sRGB color.