[css-backgrounds-3][editorial] Replace <box> definition with <visual-…

…box> reference.

css-backgrounds-3/Overview.bs

@@ -662,7 +662,7 @@ image layer.
 
 <pre class="propdef">
 Name: background-clip
-Value: <<box>>#
+Value: <<visual-box>>#
 Initial: border-box
 Applies to: all elements
 Inherited: no
@@ -673,22 +673,18 @@ Animation type: repeatable list
 
 <p>Determines the <dfn id="background-painting-area">background painting area</dfn>,
 which determines the area within which the background is painted.
-The syntax of the property is given with
-
-<pre class=prod><dfn><<box>></dfn> = border-box | padding-box | content-box</pre>
-
-<p>Values have the following meanings:
+Values have the following meanings:
 
 <dl dfn-for=background-clip dfn-type=value>
   <dt><dfn>border-box</dfn></dt>
   <dd>The background is painted within (clipped to) the
-    <span>border box.</span>
+    [=border box=].
   <dt><dfn>padding-box</dfn></dt>
   <dd>The background is painted within (clipped to) the
-    <span>padding box.</span>
+    [=padding box=].
   <dt><dfn>content-box</dfn></dt>
   <dd>The background is painted within (clipped to) the
-    <span>content box.</span>
+    [=content box=].
 </dl>
 
 <p class=note>Note that the root element has a different <span>background
@@ -714,7 +710,7 @@ layer.
 
 <pre class="propdef">
 Name: background-origin
-Value: <<box>>#
+Value: <<visual-box>>#
 Initial: padding-box
 Applies to: all elements
 Inherited: no
@@ -974,8 +970,8 @@ Animation type: see individual properties
 <p>Where
 
 <pre class=prod>
-<dfn>&lt;bg-layer></dfn> = <<bg-image>> || <<bg-position>> [ / <<bg-size>> ]? || <<repeat-style>> || <<attachment>> || <<box>> || <<box>>
-<dfn>&lt;final-bg-layer></dfn> =  <<bg-image>> || <<bg-position>> [ / <<bg-size>> ]? || <<repeat-style>> || <<attachment>> || <<box>> || <<box>> || <<'background-color'>></pre>
+<dfn>&lt;bg-layer></dfn> = <<bg-image>> || <<bg-position>> [ / <<bg-size>> ]? || <<repeat-style>> || <<attachment>> || <<visual-box>> || <<visual-box>>
+<dfn>&lt;final-bg-layer></dfn> =  <<bg-image>> || <<bg-position>> [ / <<bg-size>> ]? || <<repeat-style>> || <<attachment>> || <<visual-box>> || <<visual-box>> || <<'background-color'>></pre>
 
 <p class=note>Note that a color is permitted in
 <<final-bg-layer>>, but not in <<bg-layer>>.
@@ -996,7 +992,7 @@ that property's initial value, then assigns any explicit values specified
 for this layer in the declaration. Finally 'background-color' is set to
 the specified color, if any, else set to its initial value.
 
-<p>If one <<box>> value is present then it sets
+<p>If one <<visual-box>> value is present then it sets
 both 'background-origin' and 'background-clip' to that value.
 If two values are present, then the first sets 'background-origin'
 and the second 'background-clip'.