Added the first proposal for a 'environment-blending' keyword. (w3c#2719)

Author: rcabanier

mediaqueries-5/Overview.bs

@@ -148,6 +148,59 @@ Detecting the ambient light level: the 'light-level' feature</h3>
 		</pre>
 	</div>
 
+<h3 id="environment-blending">
+Detecting the display technology: the 'environment-blending' feature</h3>
+
+    <pre class='descdef mq'>
+    Name: environment-blending
+    Value: opaque | additive | subtractive
+    For: @media
+    Type: discrete
+    </pre>
+
+    The 'environment-blending' media feature is used to query the characteristics of the user's display
+    so the author can adjust the style of the document.
+    An author might choose to adjust the visuals and/or layout of the page depending on the display
+    technology to increase the appeal or improve legibility.
+
+    The following values are valid:
+
+    <dl dfn-type=value dfn-for="@media/environment-blending">
+        <dt><dfn>opaque</dfn>
+        <dd>
+            The document is rendered on an opaque medium, such as a traditional monitor or paper.
+            Black is dark and white is 100% light.
+
+        <dt><dfn>additive</dfn>
+        <dd>
+            The display blends the colors of the canvas with the real world using additive mixing.
+            Black is fully transparent and white is 100% light.
+
+            For example: a head-up display in a car.
+
+        <dt><dfn>subtractive</dfn>
+        <dd>
+            The display blends the colors of the canvas with the real world using subtractive mixing.
+            White is fully transparent and dark colors have the most contrast.
+
+            For example: an LCD display embedded in a bathroom mirror.
+    </dl>
+
+    Issue: Is there a need for the 'subtractive' value?
+
+    <div class="example">
+        <pre>
+        body { background-color: white; }
+        p { color: black; }
+
+        @media(environment-blending: additive) {
+            body { background-color: black; }
+            p { color: white; font-size: 16px; font-weight: 1000; }
+        }
+        </pre>
+    </div>
+
+
 
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