Editorial: clarify which document of a/which top-level browsing context

Closes #2523.

source

@@ -73583,13 +73583,11 @@ END:VCARD</pre>
   area of the document</dfn>. Which control is so designated changes over time, based on algorithms
   in this specification.</p>
 
-  <p>The <dfn>currently focused area of a top-level browsing context</dfn> at any particular time is
-  the <span>focusable area</span> returned by this algorithm:</p>
+  <p>The <dfn>currently focused area of a top-level browsing context</dfn> <var>topLevelBC</var> at
+  any particular time is the <span>focusable area</span> returned by this algorithm:</p>
 
   <ol>
-
-   <li><p>Let <var>candidate</var> be the <code>Document</code> of the <span>top-level
-   browsing context</span>.</p></li>
+   <li><p>Let <var>candidate</var> be <var>topLevelBC</var>'s <span>active document</span>.</p></li>
 
    <li><p>If the designated <span>focused area of the document</span> is a <span>browsing context
    container</span> with a non-null <span>nested browsing context</span>, then let
@@ -73601,7 +73599,6 @@ END:VCARD</pre>
    the document">focused area</span>.</p></li>
 
    <li><p>Return <var>candidate</var>.</p></li>
-
   </ol>
 
   <p>An element that is the <span>DOM anchor</span> of a <span>focusable area</span> is said to <dfn
@@ -74409,8 +74406,8 @@ END:VCARD</pre>
   <var>target</var>, are as follows:</p>
 
   <ol>
-   <li><p>Let <var>candidate</var> be the <code>Document</code> of the <span>top-level browsing
-   context</span>.</p></li>
+   <li><p>Let <var>candidate</var> be <var>target</var>'s <span>top-level browsing context</span>'s
+   <span>active document</span>.</p></li>
 
    <li>
     <p>While true:</p>