[css-color-4] Specify RGB channels using reference ranges rather than prose, for consistency

Author: svgeesus

css-color-4/Overview.bs

@@ -1143,7 +1143,8 @@ sRGB Colors</h2>
 <h3 id='rgb-functions'>
 The RGB functions: ''rgb()'' and ''rgba()''</h3>
 
-	The ''rgb()'' and ''rgba()'' functions define an sRGB color by specifying the red, green, and blue channels directly.
+	The ''rgb()'' and ''rgba()'' functions define an sRGB color 
+	by specifying the r, g and b (red, green, and blue) channels directly.
 	Their syntax is:
 
 	<pre class='prod'>
@@ -1161,6 +1162,20 @@ The RGB functions: ''rgb()'' and ''rgba()''</h3>
 		[ / [<<alpha-value>> | none] ]?  )
 	</pre>
 
+	<table id="prr-srgb">
+		<tr>
+			<th>Percentages</th>
+			<td>Allowed for r, g and b</td>
+		</tr>
+		<tr>
+			<th>Percent reference range&nbsp;</th>
+			<td>
+				For r, g and b: 0% = 0.0, 100% = 255.0
+				For alpha: 0% = 0.0, 100% = 1.0
+			</td>
+		</tr>
+	</table>
+
 	<wpt>
 		rgb-001.html
 		rgb-002.html
@@ -1176,14 +1191,13 @@ The RGB functions: ''rgb()'' and ''rgba()''</h3>
 		parsing/color-valid-rgb.html
 	</wpt>
 
-	The first three arguments specify the red, green, and blue channels of the color, respectively.
+	The first three arguments specify the r, g and b (red, green, and blue) 
+	channels of the color, respectively.
 	''0%'' represents the minimum value for that color channel in the sRGB gamut,
 	and ''100%'' represents the maximum value.
-	A <<number>> is equivalent to a <<percentage>>,
-	but with a different range:
-	''0'' again represents the minimum value for the color channel,
-	but ''255'' represents the maximum.
-	These values come from the fact that many graphics engines store the color channels internally as a single byte,
+
+	The [=percentage reference range=] of the color channels comes from the historical fact that 
+	many graphics engines stored the color channels internally as a single byte,
 	which can hold integers between 0 and 255.
 	Implementations should honor the precision of the channel as authored or calculated wherever possible.
 	If this is not possible, the channel should be <a href="https://drafts.csswg.org/css-values-4/#combine-integers">rounded towards +∞</a>.