[css-color-adjust-1] Add a little more explanation for what color-scheme is. w3c#5897

Author: tabatkins

css-color-adjust-1/Overview.bs

@@ -3,11 +3,11 @@ Title: CSS Color Adjustment Module Level 1
 Shortname: css-color-adjust
 Level: 1
 Status: ED
-Work Status: refining
+Work Status: exploring
 Group: CSSWG
 TR: https://www.w3.org/TR/css-color-adjust-1/
 ED: https://drafts.csswg.org/css-color-adjust-1/
-Previous Version: https://www.w3.org/TR/2020/WD-css-color-adjust-1-20201109/
+Previous Version: https://www.w3.org/TR/2020/WD-css-color-adjust-1-20200402/
 Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
 Editor: Rossen Atanassov, Microsoft, ratan@microsoft.com, w3cid 49885
 Editor: Rune Lillesveen, Google, futhark@google.com, w3cid 45291
@@ -115,19 +115,27 @@ Opting Into a Preferred Color Scheme: the 'color-scheme' property {#color-scheme
 	Name: color-scheme
 	Value: normal | [ light | dark | <<custom-ident>> ]+
 	Initial: normal
-	Applies to: all elements and text
+	Applies to: all elements
 	Inherited: yes
 	Computed Value: the keyword ''normal'', or an ordered list of specified color scheme keywords
 	</pre>
 
+	While the 'prefers-color-scheme' media feature
+	allows an author to adapt the page’s colors to the user’s preferred color scheme,
+	many parts of the page are not under the author's control
+	(such as form controls, scrollbars, etc).
 	The 'color-scheme' property allows an element to indicate
-	which [=color schemes=] it is comfortable being rendered with.
+	which [=color schemes=] it is designed to be rendered with.
 	These values are negotiated with the user's preferences,
-	resulting in a <dfn>used color scheme</dfn>
+	resulting in a <dfn export>used color scheme</dfn>
 	that affects UI things such as
 	the default colors of form controls and scrollbars
 	as well as the used values of the CSS system colors.
 
+	Note: Because many pages were authored before color scheme support existed,
+	user agents cannot automatically adapt the colors used in elements under their control,
+	as it might cause unreadable color contrast with the surrounding page.
+
 	Values are defined as follows:
 
 	<dl dfn-type=value dfn-for=color-scheme>
@@ -273,7 +281,7 @@ Forced Color Schemes {#forced}
 	intended to increase the readability of text through color contrast.
 	Individuals with limited vision
 	often find it more comfortable to read content
-	when there is a particular type of contrast
+	when there is a a particular type of contrast
 	between foreground and background colors.
 
 	Operating systems can provide built-in color themes,
@@ -322,7 +330,7 @@ Forced Color Schemes {#forced}
 	when '@media/forced-colors' is ''active'',
 	reducing effects such as shadows, fades, blurs, filters, gradients,
 	and image or pattern fills
-	that add complexity to discerning shape outline
+	that add complexity to discerning shape outlin
 -->
 
 Properties Affected by Forced Colors Mode {#forced-colors-properties}
@@ -346,14 +354,10 @@ Properties Affected by Forced Colors Mode {#forced-colors-properties}
 		<li>'scrollbar-color'
 		<li>'-webkit-tap-highlight-color'
 		<li>'background-color'
-		<li>'caret-color'
-		<li>'flood-color'
-		<li>'lighting-color'
-		<li>'stop-color'
 	</ul>
 
-	if its [=computed value=] is a color other than a [=system color=],
-	its [=used value=] is forced to a [=system color=] as follows:
+	if its [=computed value=] would be a color other than a [=system color=],
+	it is instead forced to a [=system color=] as follows:
 
 	* If the color value indicates a “fallback” color
 		(as in the ''color()'' function in [[CSS-COLOR-5]])
@@ -374,34 +378,11 @@ Properties Affected by Forced Colors Mode {#forced-colors-properties}
 		whenever all of the element’s affected properties
 		are likewise UA-determined.
 
-		<div class="note">
-			UAs need to be careful about inheritance when forcing colors.
-			For example,
-			suppose the UA’s button 'color' and 'background-color'
-			are the opposite of its canvas 'color' and 'background-color'.
-			Given markup such as
-
-			<xmp highlight=html>
-				<button>Push <em>this</em> button</button>
-			</xmp>
-
-			Normally, <{em}> will inherit from <{button}>,
-			ensuring its readability.
-			However in [=forced colors mode=],
-			the 'color' of both <{button}> and <{em}> will need to be forced.
-			It's easy to see that <{button}>’s color should be forced to the button color,
-			but <{em}> also needs to be forced to the button color;
-			if it were forced to the canvas 'color' like it is everywhere else in the document,
-			its text will be unreadable.
-		</div>
-
 	Additionally:
-	* 'box-shadow' and 'text-shadow' compute to ''box-shadow/none''
+	* 'box-shadow' and 'text-shadow' compute to to ''box-shadow/none''
 	* 'background-image' computes to ''background-image/none''
 		unless the original value contains a ''url()'' function
 	* 'color-scheme' computes to ''light dark''
-	* 'scrollbar-color' computes to ''scrollbar-color/auto''
-	* 'accent-color' computes to ''accent-color/auto''
 
 	UAs may further tweak these <a>forced colors mode</a> heuristics
 	to provide better user experience.
@@ -413,7 +394,7 @@ Opting Out of a Forced Color Scheme: the 'forced-color-adjust' property {#forced
 	Name: forced-color-adjust
 	Value: auto | none
 	Initial: auto
-	Applies to: all elements and text
+	Applies to: all elements
 	Inherited: yes
 	Animatable: not animatable
 	</pre>
@@ -527,12 +508,11 @@ Performance-based Color Schemes: the 'color-adjust' property {#perf}
 			when distracted in a car.
 	</dl>
 
-Privacy and Security Considerations {#priv-sec}
+Privacy and Security Considerations {#privsec}
 ===================================
 
 	Applying user color preferences via [=color schemes=] or [=forced colors mode=]
-	exposes the user's color preferences to the page
-	via {{getComputedStyle()}},
+	expose the user's color preferences to the page,
 	which can increase fingerprinting surface.
 
 	Additionally, it may be possible for an embedded document
@@ -557,13 +537,22 @@ Acknowledgements {#acknowledgements}
 Changes {#changes}
 =======
 
-	Changes since the <a href="https://www.w3.org/TR/2020/WD-css-color-adjust-1-20201109/">9 NOvember 2020 Working Draft</a>:
+	Changes since the <a href="https://www.w3.org/TR/2019/WD-css-color-adjust-1-20190523/">23 May 2019 Working Draft</a>:
 
 	<ul>
-		<li>Added 'scrollbar-color', 'caret-color', 'flood-color', 'lighting-color', 'stop-color', and 'accent-color'
-			resets to [=forced colors mode=].
-			(<a href="https://github.com/w3c/csswg-drafts/issues/5778">Issue 5778</a>,
-			 <a href="https://github.com/w3c/csswg-drafts/issues/5873">Issue 5873</a>,
+		<li>Forced background colors don't revert, they force all color channels other than alpha (to preserve author’s transparency).
+			<a href="https://github.com/w3c/csswg-drafts/issues/4175">Issue 4175</a>.
+		<li>Other properties revert by rewriting author-level rules to specify ''revert'',
+			not by injecting ''revert !important'' rules into the cascade.
+			<a href="https://github.com/w3c/csswg-drafts/issues/4020">Issue 4020</a>.
+		<li>Force opaque background if color-adjust mismatches between <{iframe}> and embedded document.
+			<a href="https://github.com/w3c/csswg-drafts/issues/4472">Issue 4472</a>.
+		<li>Don't force colors on SVG text.
+		<li>Rename ''color-scheme: auto'' to ''color-scheme: normal''.
+			<a href="https://github.com/w3c/csswg-drafts/issues/3849">Issue 3849</a>.
+		<li>Miscellaneous clarifications.
+	</ul>
+ues/5873">Issue 5873</a>,
 			 <a href="https://github.com/w3c/csswg-drafts/issues/5987">Issue 5987</a>)
 	</ul>