[css-color-4] Move alpha value definition up to opacity property, cla…

…rify opacity specified values are not clamped. #8311

css-color-4/Overview.bs

@@ -633,18 +633,34 @@ Transparency: the 'opacity' property</h3>
 	</wpt>
 
 	<dl>
-		<dt><<alpha-value>>
+		<dt><dfn dfn-for="opacity"><<alpha-value>></dfn>
 		<dd>
 			The opacity to be applied to the element.
-			It is interpreted identically to its definition in ''rgb()'',
-			except that the resulting opacity is applied to the entire element,
+			The resulting opacity is applied to the entire element,
 			rather than a particular color.
+
+			Opacity values outside the range [0,1] are not invalid,
+			and a preserved in specified values,
+			but are clamped to the range [0, 1]
+			in computed values.
 	</dl>
 
 	<wpt>
 		inline-opacity-float-child.html
 	</wpt>
 
+	Opacity in CSS is typically represented using the <<alpha-value>> syntax,
+	for example in the 'opacity' property
+	or as the [=alpha component=] in a [=color function=].
+	Represented as a <<number>>, the useful range of the value is ''0''
+	(representing full transparency)
+	to ''1''
+	(representing full opacity).
+	It can also be written as a <<percentage>>,
+	which [=computed value|computes to=]
+	the equivalent <<number>>
+	(''0%'' to ''0'', ''100%'' to ''1'').
+
 	The 'opacity' property applies the specified opacity to the element <em>as a whole</em>,
 	including its contents,
 	rather than applying it to each descendant individually.
@@ -962,25 +978,14 @@ Legacy (Comma-separated) Color Function Syntax</h4>
 	the <a>legacy color syntax</a> is invalid.
 
 <h3 id="alpha-syntax">
-Representing Transparency: the <<alpha-value>> syntax</h3>
+Representing Transparency in Colors: the <<alpha-value>> syntax</h3>
 
 	<pre class="prod">
-	<dfn>&lt;alpha-value></dfn> = <<number>> | <<percentage>>
+	<dfn dfn-for="color">&lt;alpha-value></dfn> = <<number>> | <<percentage>>
 	</pre>
 
-	Opacity in CSS is typically represented using the <<alpha-value>> syntax,
-	for example in the 'opacity' property
-	or as the [=alpha component=] in a [=color function=].
-	Represented as a <<number>>, the useful range of the value is ''0''
-	(representing full transparency)
-	to ''1''
-	(representing full opacity).
-	It can also be written as a <<percentage>>,
-	which [=computed value|computes to=]
-	the equivalent <<number>>
-	(''0%'' to ''0'', ''100%'' to ''1'').
 	Unless otherwise specified,
-	an <<alpha-value>> component defaults to ''100%'' when omitted.
+	an <<alpha-value>> component of a color defaults to ''100%'' when omitted.
 	Values outside the range [0,1] are not invalid,
 	but are clamped to that range at parsed-value time.