[mediaqueries-5] Add initial versions of prefers-contrast and color-scheme

Author: grorg

mediaqueries-5/Overview.bs

@@ -561,6 +561,78 @@ Detecting the desire for reduced transparency on the page: the 'prefers-reduced-
 
 	</dl>
 
+<h3 id="prefers-contrast">
+Detecting the desire for increased or decreased color contrast from elements on the page: the 'prefers-contrast' feature</h3>
+
+	<pre class='descdef mq'>
+	Name: prefers-contrast
+	Value: no-preference | high | low
+	For: @media
+	Type: discrete
+	</pre>
+
+	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.
+
+	<dl dfn-type=value dfn-for="@media/prefers-contrast">
+		<dt><dfn>no-preference</dfn>
+		<dd>
+			Indicates that the user has made no preference known
+			to the system. This keyword value evaluates as false
+			in the <a>boolean context</a>.
+
+		<dt><dfn>high</dfn>
+		<dd>
+			Indicates that user has notified the system that they
+			prefer an interface that has a higher level of contrast.
+
+		<dt><dfn>low</dfn>
+		<dd>
+			Indicates that user has notified the system that they
+			prefer an interface that has a lower level of contrast.
+
+	</dl>
+
+	Issue: Should we include 'forced-low' and 'forced-high' values? We don't necessarily want the
+	page to try to undo what the system might be enforcing.
+
+<h3 id="prefers-color-scheme">
+Detecting the desire for increased or decreased color contrast from elements on the page: the 'prefers-color-scheme' feature</h3>
+
+	<pre class='descdef mq'>
+	Name: prefers-color-scheme
+	Value: no-preference | light | dark
+	For: @media
+	Type: discrete
+	</pre>
+
+	The 'prefers-color-scheme' media feature is used to detect if the user
+	has requested the system use a light or dark color theme.
+
+	<dl dfn-type=value dfn-for="@media/prefers-color-scheme">
+		<dt><dfn>no-preference</dfn>
+		<dd>
+			Indicates that the user has made no preference known
+			to the system. This keyword value evaluates as false
+			in the <a>boolean context</a>.
+
+		<dt><dfn>light</dfn>
+		<dd>
+			Indicates that user has notified the system that they
+			prefer an interface that has a light theme.
+
+		<dt><dfn>dark</dfn>
+		<dd>
+			Indicates that user has notified the system that they
+			prefer an interface that has a dark theme.
+
+	</dl>
+
+	Issue: Should we include 'forced-light' and 'forced-dark' values? We don't necessarily want the
+	page to try to undo what the system might be enforcing.
 
 <h2 id="changes" class="no-num">
 Changes</h2>
@@ -579,7 +651,13 @@ The following changes were made to this specification since the
 		Add 'prefers-reduced-motion' media feature.
 
 	<li>
-		Add 'prefers-reduced-transparency' media feature.		
+		Add 'prefers-reduced-transparency' media feature.
+
+	<li>
+		Add 'prefers-contrast' media feature.
+
+	<li>
+		Add 'prefers-color-scheme' media feature.
 
 </ul>