Address review feedback

fetch.bs

@@ -4979,17 +4979,22 @@ steps:
      <li><p>Let <var>requestEnvironment</var> be the result of
      <a for=request>determining the environment</a> given <var>request</var>.
 
-     <li><p>Let <var>isNavigation</var> be true if <var>request</var>'s <a for=request>mode</a> is
-     not "<code>navigate</code>"; otherwise, false.
+     <li><p>Let <var>isTopLevelNavigation</var> be true if <var>request</var>'s <a
+     for=request>destination</a> is "<code>document</code>"; otherwise, false.
 
-     <li><p>If <var>isNavigation</var> is false and <var>requestEnvironment</var> is null, then
-     return a <a>network error</a>.
+     <li><p>If <var>isTopLevelNavigation</var> is false and <var>requestEnvironment</var> is null,
+     then return a <a>network error</a>.
+
+     <li><p>Let <var>blob</var> be null.
+
+     <li><p>If <var>isTopLevelNavigation</var> is true, then set <var>blob</var> to the result of
+     <a>obtaining a blob object</a> given <var>blobURLEntry</var> and the string
+     "<code>navigation</code>".
 
-     <li><p>Let <var>blob</var> be the result of <a>obtaining a blob object</a> given
-     <var>blobURLEntry</var>, <var>requestEnvironment</var>, and <var>isNavigation</var>.
+     <li><p>Otherwise, set <var>blob</var> to the result of <a>obtaining a blob object</a> given
+     <var>blobURLEntry</var> and <var>requestEnvironment</var>.
 
-     <li><p>If <var>blob</var> is failure, or <var>blob</var> is not a {{Blob}} object, then
-     return a <a>network error</a>.
+     <li><p>If <var>blob</var> is not a {{Blob}} object, then return a <a>network error</a>.
 
      <li><p>Let <var>response</var> be a new <a for=/>response</a>.