[css-color-4] Factor out <alpha-value> into its own section.

Author: fantasai

css-color-4/Overview.bs

@@ -760,6 +760,29 @@ Legacy Comma-separated Color Function Syntax</h4>
 	where there is no Web compatibility issue,
 	the <a>legacy color syntax</a> is invalid.
 
+<h3 id="alpha-syntax">
+Representing Transparency: the <<alpha-value>> syntax</h3>
+
+	<pre class="prod">
+	<dfn>&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.
+	Values outside the range [0,1] are not invalid,
+	but are clamped to that range when [=computed value|computed=].
+
 <h3 id="hue-syntax">
 Representing Cylindrical-coordinate Hues: the <<hue>> syntax</h3>
 
@@ -1685,7 +1708,6 @@ The RGB functions: ''rgb()'' and ''rgba()''</h3>
 	<pre class='prod'>
 	<dfn>rgb()</dfn> = rgb( [<<percentage>> | none]{3} [ / [<<alpha-value>> | none] ]? ) |
 	  rgb( [<<number>> | none]{3} [ / [<<alpha-value>> | none] ]? )
-	<dfn>&lt;alpha-value></dfn> = <<number>> | <<percentage>>
 	</pre>
 
 	<wpt>
@@ -1714,12 +1736,6 @@ The RGB functions: ''rgb()'' and ''rgba()''</h3>
 	If this is not possible, the channel should be <a href="https://drafts.csswg.org/css-values-4/#combine-integers">rounded towards +∞</a>.
 
 	The final argument, the <<alpha-value>>, specifies the alpha of the color.
-	If given as a <<number>>, the useful range of the value is ''0''
-	(representing a fully transparent color)
-	to ''1''
-	(representing a fully opaque color).
-	If given as a <<percentage>>, ''0%'' represents a fully transparent color,
-	while ''100%'' represents a fully opaque color.
 	If omitted, it defaults to ''100%''.
 
 	<wpt>
@@ -3654,9 +3670,9 @@ Specifying Lab and LCH: the ''lab()'' and ''lch()'' functional notations</h3>
 	and theoretically unbounded
 	(but in practice do not exceed ±160).
 
-	There is an optional fourth alpha value,
+	There is an optional fourth <<alpha-value>> component,
 	separated by a slash,
-	and interpreted identically to the <<alpha-value>> in ''rgb()''.
+	representing the [=alpha component=].
 
 	If the lightness of a Lab color is ''0%'',
 	both the a and b components are [=powerless=].
@@ -3730,9 +3746,9 @@ Specifying Lab and LCH: the ''lab()'' and ''lch()'' functional notations</h3>
 	''180deg'' points along the negative "a" axis (toward greenish cyan),
 	and ''270deg'' points along the negative "b" axis (toward sky blue).
 
-	There is an optional fourth alpha value,
+	There is an optional fourth <<alpha-value>> component,
 	separated by a slash,
-	and interpreted identically to the <<alpha-value>> in ''rgb()''.
+	representing the [=alpha component=].
 
 	If the chroma of an LCH color is ''0%'',
 	the hue component is [=powerless=].
@@ -3818,9 +3834,9 @@ Specifying Lab and LCH: the ''lab()'' and ''lch()'' functional notations</h3>
 	and theoretically unbounded
 	(but in practice do not exceed ±0.5).
 
-	There is an optional fourth alpha value,
+	There is an optional fourth <<alpha-value>> component,
 	separated by a slash,
-	and interpreted identically to the <<alpha-value>> in ''rgb()''.
+	representing the [=alpha component=].
 
 	If the lightness of an OKLab color is ''0%'',
 	both the a and b components are [=powerless=].
@@ -3891,9 +3907,9 @@ Specifying Lab and LCH: the ''lab()'' and ''lch()'' functional notations</h3>
 		''180deg'' points along the negative "a" axis (toward greenish cyan),
 		and ''270deg'' points along the negative "b" axis (toward sky blue).
 
-		There is an optional fourth alpha value,
+		There is an optional fourth <<alpha-value>> component,
 		separated by a slash,
-		and interpreted identically to the <<alpha-value>> in ''rgb()''.
+		representing the [=alpha component=].
 
 		If the chroma of an OKLCH color is ''0%'',
 		the hue component is [=powerless=].
@@ -4072,8 +4088,6 @@ Specifying Predefined Colors: the ''color()'' function</h3>
 
 
 	* An optional slash-separated <<alpha-value>>.
-		This is interpreted the same way as the <<alpha-value>> in ''rgb()'',
-		and if omitted it defaults to ''100%''.
 
 	<wpt>
 		parsing/color-valid.html
@@ -6108,6 +6122,14 @@ parsing/relative-color-valid.html
 <h2 id='changes' class='no-num'>
 Changes</h2>
 
+<h3 id="changes-from-20220705">Changes since the
+	<a href="https://www.w3.org/TR/2022/CR-css-color-4-20220705/">Candidate Recommendation of 5 July 2022</a>
+</h3>
+
+<ul>
+	<li>Editorial refactoring.
+</ul>
+
 <h3 id="changes-from-20220628">Changes since the
 	<a href="https://www.w3.org/TR/2022/WD-css-color-4-20220628/">Working Draft of 28 June 2022</a>
 </h3>