[css-color-4] Rewrite computed/used colors section and fill in more detail. Fixes w3c#4136, fixes w3c#3843.

Author: tabatkins

css-color-4/Overview.bs

@@ -13,7 +13,6 @@ Editor: Chris Lilley, W3C, chris@w3.org, w3cid 1438
 Former Editor: L. David Baron, Mozilla https://www.mozilla.org/, https://dbaron.org/, w3cid 15393
 Abstract: This specification describes CSS <<color>> values and properties for foreground color and group opacity.
 Repository: w3c/csswg-drafts
-Inline Github Issues: title
 Ignored Terms: stacking context, double, octet
 </pre>
 
@@ -181,60 +180,74 @@ Notes On Using Colors</h3>
 <h2 id='resolving-color-values'>
 Resolving Color values</h2>
 
-	Various properties accept <<color>> values.
-	Unless an exception is explicitly defined,
-	all such properties must <dfn export lt="resolve color values|resolving color values">resolve color values</dfn> as defined below
-	to determine the <a>computed value</a> and the <a>used value</a> for <<color>>.
-
-	<ul>
-		<li>
-		If ''<color>/currentcolor'' is the specified value of the 'color' property,
-		it is treated as if the specified value was ''inherit''.
-
-		For all other properties that accept a <<color>>,
-		the computed value of the ''<color>/currentcolor'' keyword is ''<color>/currentcolor'',
-		and the used value of ''<color>/currentcolor'' is the same as
-		the used value of the 'color' property on the same element.
+	Unless otherwise specified for a particular property,
+	[=specified value|specified=] colors are resolved to
+	<dfn export lt="computed color">[=computed value|computed=] colors</dfn>
+	and then further to <dfn export lt="used color">[=used value|used=] colors</dfn> as follows:
+
+	: ''transparent''
+	::
+		The computed and used value is [=transparent black=].
+
+	: [=hex colors=]
+	: ''rgb()'' and ''rgba()'' values
+	: ''hsl()'' and ''hsla()'' values
+	: ''hwb()'' values
+	: [=named colors=]
+	::
+		The computed and used value
+		is the corresponding sRGB color
+		paired with the specified alpha channel
+		(defaulting to opaque if unspecified).
+
+	: ''lab()'', ''lch()'', and ''gray()'' values
+	::
+		The computed and used value
+		is the corresponding CEI Lab color
+		paired with the specified alpha channel
+		(defaulting to opaque if unspecified).
+
+		Issue(3844): Does working color space affect these values?
+
+	: ''color()'' values
+	::
+		The computed and used value
+		is the color in the specified colorspace,
+		paired with the specified alpha channel
+		(defaulting to opaque if unspecified).
+
+	: ''device-cmyk()'' values
+	::
+		The computed and used value
+		is the specified device-specific CMYK color,
+		paired with the specified alpha channel
+		(defaulting to opaque if unspecified).
+
+		The [=actual value=] can vary based on the operation;
+		for rendering to a CMYK-capable device,
+		it may be rendered as a CMYK color;
+		for blending with non-CMYK colors
+		or rendering to a non-CMYK device,
+		it must be converted
+		as specified in [[#cmyk-colors]].
+
+	: ''currentcolor''
+	::
+		The ''currentcolor'' keyword computes to itself.
+
+		In the 'color' property,
+		its used value is the [=inherited value=].
+		In any other property,
+		its used value is the used value of the 'color' property on the same element.
 
 		Note: This means that if the ''<color>/currentcolor'' value is inherited,
 		it’s inherited as a keyword,
 		not as the value of the 'color' property,
 		so descendants will use their own 'color' property to resolve it.
 
-		<li>
-		The computed value and used value of ''<color>/transparent'' is ''rgba(0, 0, 0, 0)''.
-
-		Issue(3844):
-		<!-- needs WPT test -->
-
-		<li>
-		The computed value and used value of
-		<a>named colors</a> (including <<system-color>> colors),
-		3 and 6 digits <a>hex colors</a>,
-		4 and 8 digits <a>hex colors</a> with an explicitly opaque alpha channel,
-		comma separated ''rgb()'' colors without an alpha channel,
-		comma separated ''rgba()'' colors with an explicitly opaque alpha channel,
-		comma separated ''hsl()'' colors without an alpha channel,
-		and comma separated ''hsla()'' colors with an explicitly opaque alpha channel,
-		is the equivalent numeric value in comma separated ''rgb()'' notation omitting the alpha value.
-
-		<li>
-		The computed value and used value of
-		4 and 8 digits <a>hex colors</a> with a non opaque alpha channel,
-		comma separated ''rgba()'' colors with a non opaque alpha channel,
-		and comma separated ''hsla()'' colors with a non opaque alpha channel,
-		is the equivalent numeric value in comma separated ''rgba()'' notation with the alpha value.
-
-	</ul>
-
-	Issue(3843):
-
-	Issue(3844):
-
-	Issue(3845):
+	The [=resolved value=] of a <<color>> is its [=used value=].
 
-	Any future specification extending the syntax of <<color>>
-	must define the how to <a>resolve color values</a> for the new extensions.
+	Issue(3845): When should channel-clamping occur?
 
 <h2 id='numeric-rgb'>
 RGB Colors</h2>