[css-color-5] Clarified that RCS color components are not clamped, while RCS alpha is #9805

Author: svgeesus

css-color-5/Overview.bs

@@ -946,11 +946,49 @@ so it has meaningful values for the channels.</p>
 	regardless of what the [=origin color's=] opacity was.
 </div>
 
-<div class=example>
-	While most uses of [=relative color=] syntax
-	will use the [=channel keywords=] in their corresponding argument,
-	you can use them in any position.
+When relative color syntax is used,
+color channel values, 
+whether directly specified 
+or arising from color space conversion,
+are <em>not</em> clamped to the reference ranges but are retained as-is.
+This preserves out of gamut values,
+if the destination color space is capable of representing them.
+
+<div class="example">
+	For example, a Display P3 color
+	which is outside the gamut of sRGB can still be represented,
+	as it is not clipped.
+
+	<pre highlight=css>
+		--vivid-yellow: <span class="swatch oog" style="--color: color(display-p3 1 1 0)"></span> color(display-p3 1 1 0); 
+		--paler-yellow: <span class="swatch" style="--color: rgb(100% 100% 15.37%)"></span> srgb(from var(--vivid-yellow) r g calc(b + 50%));
+	</pre>
+
+	Here --vivid-yellow, once converted to sRGB, 
+	is <span class="swatch oog" style="--color: color(display-p3 1 1 0)"></span> rgb(100% 100% -34.63%)
+	and the negative blue component is not clamped.
+	The result of the RCS calculation is 
+	<span class="swatch" style="--color: rgb(100% 100% 15.37%)"></span> rgb(100% 100% 15.37%)
+</div>
+
+However, when relative color syntax is used,
+alpha channels <em>are</em> clamped to the reference range.
 
+<div class="example">
+	For example, attempting to double an alpha of 0.7 in the origin color
+	results in an alpha in the result of 1, not 1.4.
+
+	<pre highlight=css>
+		--tan: <span class="swatch" style="--color: rgb(80.93% 70% 55.27% / 70%)"></span> oklch(78% 0.06 75) / 0.7;
+		--deeper-tan: <span class="swatch" style="--color: rgb(80.93% 70% 55.27%)"></span> oklch(from var(--tan) l c h / calc(alpha * 2));
+	</pre>
+</div>
+
+While most uses of [=relative color=] syntax
+will use the [=channel keywords=] in their corresponding argument,
+you can use them in any position.
+
+<div class=example>
 	For example, to do a rough approximation of grayscaling a color:
 
 	<pre highlight=css>