[css-backgrounds-4] Added background-layer shorthand property

Author: SebastianZ

css-backgrounds-4/Overview.bs

@@ -185,6 +185,54 @@ Painting Area: the 'background-clip' property</h3>
 		</dd>
 	</dl>
 
+<h3 id='background-layers'>
+Background Image Layers: the 'background-layer' shorthand property</h3>
+
+	<pre class="propdef">
+		Name: background-layer
+		Value: <<bg-layer>>#
+		Initial: see individual properties
+		Applies to: all elements
+		Inherited: no
+		Percentages: see individual properties
+		Computed value: see individual properties
+		Animation type: see individual properties
+	</pre>
+
+	<p>The 'background-layer' property is a
+	shorthand property for setting most background properties at the same
+	place in the style sheet. It covers basically the same as 'background',
+	i.e. it allows to define all the background layers. The only difference
+	is that it doesn't set the 'background-color'.
+
+	<div class="example" id="background-layer-example">
+		This example sets three background layers,
+		the first one including the image, position and repetition,
+		the second including the image, position, and size,
+		and the third one only consisting of the image.
+
+		<pre class="lang-css">
+		p {
+			background-layer:
+				url(a.png) top left no-repeat,
+				url(b.png) center / 100% 100% no-repeat,
+				url(c.png);
+		}
+		</pre>
+	</div>
+
+	<div class="invalid example" id="invalid-background-layer-example">
+		This example tries to set the background color in addition to
+		the background image. For that to work, 'background' needs
+		to be used instead of 'background-layer'.
+
+		<pre class="lang-css">
+		p {
+			background-layer: url(c.png) white;
+		}
+		</pre>
+	</div>
+
 <h2 id="changes">
 Changes</h2>
 
@@ -196,6 +244,7 @@ Additions Since [[CSS3BG]]</h3>
 	<ul>
 		<li>logical 'background-position' values (''background-position/start'', ''background-position/end'')
 		<li>the ''extend'' keyword of 'background-repeat'
+		<li>Added 'background-layer' property
 	</ul>
 
 <h2 id="acknowledgments">Acknowledgments</h2>