[css-backgrounds-4] Add propdef table for 'background-position' so we can add keywords to it.

Author: fantasai

css-backgrounds-4/Overview.bs

@@ -23,6 +23,37 @@ Introduction</h2>
 		as this will reduce the effort of keeping them in sync
 		(source diffs will be accurate in reflecting the differences).
 
+<h2 id="backgrounds">
+Backgrounds</h2>
+
+<h3 id="the-background-position">
+Background Positioning: the 'background-position' property</h3>
+
+	<pre class='propdef'>
+		Name: backround-position
+		Value: <<position>>#
+		Initial: top left
+		Applies to: all
+		Inherited: no
+		Percentages: refer to size of background positioning area <em>minus</em> size of background image
+		Media: visual
+		Computed value: A list, each item consisting of: a pair of offsets and an origin, each offset given as a combination of an absolute length and a percentage
+	</pre>
+
+	See [[CSS3BG]] for definition.
+	<p>Where
+	<pre class=prod><dfn><var>&lt;position&gt;</var></dfn> = [
+	  [ left | center | right | top | bottom | <var>&lt;percentage&gt;</var> | <var>&lt;length&gt;</var> ]
+	|
+	  [ left | center | right | <var>&lt;percentage&gt;</var> | <var>&lt;length&gt;</var> ]
+	  [ top | center | bottom | <var>&lt;percentage&gt;</var> | <var>&lt;length&gt;</var> ]
+	|
+	  [ center | [ left | right ] [ <var>&lt;percentage&gt;</var> | <var>&lt;length&gt;</var> ]? ] &amp;&amp;
+	  [ center | [ top | bottom ] [ <var>&lt;percentage&gt;</var> | <var>&lt;length&gt;</var> ]? ]
+	]</pre>
+
+	<p class="issue">Add logical keywords
+
 <h2 id="corners">
 Corners</h2>
 
@@ -104,7 +135,7 @@ Corner Shape and Size: the 'corners' shorthand</h3>
 		Name: corners
 		Value: <<'corner-shape'>> || <<'border-radius'>>
 		Initial: see individual properties
-		Applies to: <a>grid containers</a>
+		Applies to: see individual properties
 		Inherited: see individual properties
 		Percentages: see individual properties
 		Media: visual