[css-backgrounds-3][css-shapes-1][css-lists-3] Generalize computed <<image>> lines. w3c#4042

Author: fantasai

css-backgrounds-3/Overview.bs

@@ -252,7 +252,7 @@ value associated with the bottom-most background image layer.
       <td>N/A
     <tr>
       <th>Computed value:
-      <td>as specified, but with URIs made absolute
+      <td>computed <<image>>
     <tr>
       <th>Animation type:
       <td>discrete
@@ -2210,7 +2210,7 @@ this:
     <td>N/A
   <tr>
     <th>Computed value:
-    <td>the keyword ''border-image-source/none'' or the specified image with URIs made absolute
+    <td>the keyword ''border-image-source/none'' or the computed <<image>>
   <tr>
     <th>Animation type:
     <td>discrete

css-lists-3/Overview.bs

@@ -240,7 +240,7 @@ Image Markers: the 'list-style-image' property</h3>
 	Applies to: <a>list items</a>
 	Inherited: yes
 	Percentages: n/a
-	Computed value: computed value of the <<image>>, or ''list-style-image/none''
+	Computed value: the keyword ''list-style-image/none''or the computed <<image>>
 	Animation type: discrete
 	</pre>
 

css-shapes-1/Overview.bs

@@ -846,7 +846,7 @@ Float Area Shape: the 'shape-outside' property</h3>
 		Initial: none
 		Applies to: floats
 		Inherited: no
-		Computed value: as <a href="#basic-shape-computed-values">defined</a> for <<basic-shape>> (with <<shape-box>> following, if supplied), the <<image>> with its URI made absolute, otherwise as specified.
+		Computed value: as <a href="#basic-shape-computed-values">defined</a> for <<basic-shape>> (with <<shape-box>> following, if supplied); else the computed <<image>>; else the keyword as specified
 		Animation type: as <a href="#basic-shape-interpolation">defined</a> for <<basic-shape>>, otherwise discrete
 	</pre>