Refactoring of the forced-colors and prefers-contrast media feature (#5434)

This editorial reorganization of the text is intended to make the
overlap between forced-colors:active and prefers-contrast:forced
more readily understandable: one being the syntax that the CSS Working
Group finds more desirable, the other being retained for compatibility
with content issued against an earlier draft (see #3856).

Prior to this refactoring, the definition of this mode was also spread
between the two media features, causing confusion. This commits
consolidates the whole thing in one place.

Related to #5433

Author: frivoal

mediaqueries-5/Overview.bs

@@ -2624,7 +2624,7 @@ Detecting the desire for reduced transparency on the page: the 'prefers-reduced-
 	ISSUE: How does this interact with preferences around e.g. pattern fills and backgrounds?
 	They're not about transparency, but they also interfere with shape recognition.
 
-
+ oldids="forced-colors">
 Detecting the desire for increased or decreased color contrast from elements on the page: the 'prefers-contrast' feature
 
 	
@@ -2634,11 +2634,12 @@ Detecting the desire for increased or decreased color contrast from elements on
 	Type: discrete
 	
 
-	The 'prefers-contrast' media feature is used to detect if the user
-	has requested the system increase or decrease the amount of contrast
-	between adjacent colors. For example, many users have difficulty
-	reading text that has a small difference in contrast to the text
-	background and would prefer a larger contrast.
+	The 'prefers-contrast' media feature is used to detect
+	if the user has requested more or less contrast in the page.
+	This could be responded to, for example,
+	by adjusting the contrast ratio between adjacent colors,
+	or by changing how much elements stand out visually,
+	such as by adjusting their borders.
 
 	
 		no-preference
@@ -2659,10 +2660,12 @@ Detecting the desire for increased or decreased color contrast from elements on
 
 		forced
 		
-			Indicates that forced colors mode is active,
-			identically to ''forced-colors: active''.
-			See [[#forced-colors]] and
-			[[css-color-adjust-1#forced]].
+			Indicates that forced colors mode is active:
+			the user agent enforces a user-chosen limited color palette on the page,
+			in effect also implying a strong preference for the associated contrast.
+			The UA will provide the color palette to authors
+			through the CSS system color keywords.
+			See [[css-color-adjust-1#forced]] for details.
 
 
 				This does not necessarily indicates
@@ -2673,10 +2676,18 @@ Detecting the desire for increased or decreased color contrast from elements on
 				or some other arrangement that is neither particularly low or high contrast.
 			
 
-			Note: When the User Agent can determine whether the particular forced color scheme
-			chosen by the user is high or low contrast,
-			one of ''prefers-contrast: more'' or ''prefers-contrast: less'' should match,
+			Additionally, when the user agent can determine
+			whether the forced color palette chosen by the user
+			has a high or low contrast,
+			one of ''prefers-contrast: more'' or ''prefers-contrast: less'' must match
 			in addition to ''prefers-contrast: forced''.
+
+			Note:
+			Similarly,
+			if the forced color palette chosen by the user
+			fits within one of the color schemes described by 'prefers-color-scheme',
+			the corresponding value will also match.
+			See [[css-color-adjust-1#forced]] for details.
 	
 
 
@@ -2702,6 +2713,51 @@ Detecting the desire for increased or decreased color contrast from elements on
 		result in a high or low contrast (or something else).
 	
 
+
+		Preference for more or less contrast may arise
+		from a variety of different situations.
+		Here are some examples:
+
+		
+			
+				Many users have difficulty
+				reading text that has a small difference in contrast to the text
+				background and would prefer a larger contrast.
+
+			
+				People suffering from migraine
+				may find strongly contrasting pages
+				to be visually painful
+				and would prefer a low contrast.
+
+			
+				Some people with dyslexia find high contrast text hard to read,
+				as they feel that the letters shine / sparkle as if backlit by too bright a light,
+				and find low contrast to be more comfortable.
+
+			
+				Environmental factors may also lead
+				a user to prefer more or less contrast.
+				See also [[#auto-pref]].
+		
+
+		Issue: This list should be refined and expanded.
+	
+
+	For compatibility with legacy content,
+	the following syntax is also supported:
+
+	
+	Name: forced-colors
+	Value: none | active
+	For: @media
+	Type: discrete
+	
+
+	active matches
+	when ''prefers-contrast: forced'' matches,
+	otherwise none matches.
+
 
 Detecting the desire for light or dark color schemes: the 'prefers-color-scheme' feature
 
@@ -2763,36 +2819,6 @@ Detecting the desire for light or dark color schemes: the 'prefers-color-scheme'
 		please contact the CSSWG to discuss this.
 	
 
-
-Detecting a forced color palette: the 'forced-colors' feature
-
-	
-	Name: forced-colors
-	Value: none | active
-	For: @media
-	Type: discrete
-	
-
-	The 'forced-colors' media feature is used to detect if
-	the user agent has enabled a forced colors mode
-	where it enforces a user-chosen limited color palette on the page.
-
-	
-		none
-		
-			Forced colors mode is not active;
-			the page's colors are not being forced into a limited palette.
-
-		active
-		
-			Indicates that forced colors mode is active.
-			The UA will provide the color palette to authors
-			through the CSS system color keywords
-			and, if appropriate, trigger the appropriate value of 'prefers-color-scheme'
-			so that authors can adapt the page.
-			See [[css-color-adjust-1#forced]] for details.
-	
-
 
 Detecting the desire for reduced data usage when loading a page: the 'prefers-reduced-data' feature
 
@@ -3212,4 +3238,3 @@ Comments from
  akklesed,
  and 張俊芝
 improved this specification.
-