[mediaqueries-5] prefers-contrast: custom

frivoal · frivoal · commit f9f81bf0d3b4 · 2021-06-03T11:40:12.000+09:00
See w3c#6036
diff --git a/mediaqueries-5/Overview.bs b/mediaqueries-5/Overview.bs
@@ -2666,6 +2666,27 @@ Detecting the desire for increased or decreased color contrast from elements on
 		<dd>
 			Indicates that user has notified the system that they
 			prefer an interface that has a higher level of contrast.
+
+		<dt><dfn>custom</dfn>
+		<dd>
+			Indicates that the user has indicated
+			wanting a specific set of colors to be used,
+			but the contrast implied by these particular colors
+			is such that neither ''more'' nor ''less'' match.
+
+			Note: This value will match for users of [=forced colors mode=]
+			who have picked a palette that is neither particularly high nor low
+			contrast.
+			See [[#forced-colors]].
+
+			<div class=example>
+				A user calling for
+				<span style="background: #B64000; color: #00FFFF;">cyan text over a rust background</span>
+				is not--
+				at least in terms of luminosity--
+				expressing a need for particularly high or low contrast,
+				but this is not a lack of a preference either.
+			</div>
 	</dl>
 
 	<div class=note>
@@ -2677,14 +2698,22 @@ Detecting the desire for increased or decreased color contrast from elements on
 		to apply high contrast styles is incorrect and user-hostile,
 		as it would also impose high contrast styles to people who have requested the exact opposite.
 
-		However, it is also common to reduce visual clutter
+		However, it is also common to reduce visual clutter and color complexity
 		in response to both high and low contrast preferences.
 		In that case, it is appropriate to use <code class=lang-css>@media (prefers-contrast) { … }</code>
 		without specifying ''prefers-contrast/more'' or ''prefers-contrast/less'',
 		to do things like replacing background images with plain colors,
 		turning off decorative gradients,
 		or replacing border images or box shadows with simple solid borders.
-		See also [[#forced-colors]].
+		As ''prefers-contrast: custom''--
+		like ''prefers-contrast: more'' or ''prefers-contrast: less''--
+		evaluates to true in a [=boolean context=],
+		such simplifications would also benefit users of [=forced colors mode=],
+		even when their colors of choice do not result
+		in a particularly high or low contrast.
+		This is desirable,
+		as the reduced palette enforced by [=forced colors mode=]
+		calls for some visual simplification of the page.
 	</div>
 
 	<div class=example>
@@ -2746,17 +2775,19 @@ Detecting Forced Colors Mode: the 'forced-colors' feature</h3>
 				or some other arrangement that is neither particularly low or high contrast.
 			</div>
 
-			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 ''forced-colors: active''.
+			In addition to ''forced-colors: active'',
+			the user agent must also match
+			one of ''prefers-contrast: more''
+			or ''prefers-contrast: less''
+			if it can determine
+			that the forced color palette chosen by the user
+			has a particularly high or low contrast,
+			and must make ''prefers-contrast: custom'' match otherwise.
 
 			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 must also match.
-			See [[css-color-adjust-1#forced]] for details.
 
 		<dt><dfn>none</dfn>
 		<dd>
@@ -2771,18 +2802,6 @@ Detecting Forced Colors Mode: the 'forced-colors' feature</h3>
 		using the ''forced-colors'' media feature to detect when it is appropriate to do so.
 	</div>
 
-	<div class=example>
-		The reduced palette enforced by [=forced colors mode=]
-		can call for some visual simplification of the page.
-		''@media (forced-colors) or (prefers-contrast) { … }''
-		could thus be a useful query to conditionally apply styles that reduce visual clutter,
-		catching all users of forced colors and all users with contrast preferences.
-		''@media (prefers-contrast) { … }'' would leave out forced-colors users
-		with a color scheme that is neither particularly high nor low contrast,
-		while ''@media (forced-colors) { … }'' would instead leave out users with contrast preferences
-		that do not come from usage of [=forced colors mode=].
-	</div>
-
 <h3 id="prefers-color-scheme">
 Detecting the desire for light or dark color schemes: the 'prefers-color-scheme' feature</h3>
 
