collection: use instance checks

Fixes one of the problems identified in
#1347.

index.html

@@ -5796,13 +5796,13 @@ <h3>Executing Script</h3>
 
 <ul>
 <li><a>initial value</a> of the <code>toString</code> <a>own property</a> is <code>Arguments</code>
-<li>type is <a>Array</a>
-<li>type is <a><code>FileList</code></a>
-<li>type is <a><code>HTMLAllCollection</code></a>
-<li>type is <a><code>HTMLCollection</code></a>
-<li>type is <a><code>HTMLFormControlsCollection</code></a>
-<li>type is <a><code>HTMLOptionsCollection</code></a>
-<li>type is <a><code>NodeList</code></a>
+<li>instance of <a>Array</a>
+<li>instance of <a><code>FileList</code></a>
+<li>instance of <a><code>HTMLAllCollection</code></a>
+<li>instance of <a><code>HTMLCollection</code></a>
+<li>instance of <a><code>HTMLFormControlsCollection</code></a>
+<li>instance of <a><code>HTMLOptionsCollection</code></a>
+<li>instance of <a><code>NodeList</code></a>
 </ul>
 
 <p>