Editorial: add more explanation on match results

Co-Authored-By: Michael Ficarra <github@michael.ficarra.me>

spec.html

@@ -34921,7 +34921,7 @@ <h1>String.prototype.match ( _regexp_ )</h1>
 
       <emu-clause id="sec-string.prototype.matchall">
         <h1>String.prototype.matchAll ( _regexp_ )</h1>
-        <p>This method performs a regular expression match of the String representing the *this* value against _regexp_ and returns an iterator. Each iteration result's value is an Array containing the results of the match.</p>
+        <p>This method performs a regular expression match of the String representing the *this* value against _regexp_ and returns an iterator that yields match results. Each match result is an Array containing the matched portion of the String as the first element, followed by the portions matched by any capturing groups. If the regular expression never matches, the returned iterator does not yield any match results.</p>
         <p>It performs the following steps when called:</p>
 
         <emu-alg>