Phrase better

Co-authored-by: Henrik Skupin <[email protected]>

Author: yezhizhen

index.html

@@ -4585,7 +4585,7 @@ <h3>Interactability</h3>
 
 <ol>
  <li><p>Let <var>rectangle</var> be
-  the first element of the {{DOMRect}} sequence
+  the first object of the {{DOMRect}} collection
   returned by calling {{Element/getClientRects()}} on <a><var>element</var></a>.
 
  <li><p>Let <var>left</var> be