[Shadow DOM] [Bug 27876] Make it clear that changes to DOM must not a…

…ffect the event.path.

spec/shadow/index.html

@@ -1361,6 +1361,7 @@ <h3>Extensions to <code>Event</code> Interface</h3>
             <p>
               On getting, the attribute <strong>must</strong> create and return a new JavaScript Array object,
               that <strong>must</strong> be equivalent of the result of the <a>event path calculation algorithm</a> with the <a>context object</a> and the <a>event target</a> which is not adjusted by the <a>retargeting algorithm</a> as input if the event is being dispatched.
+              This <a>event path calculation algorithm</a> <strong>must</strong> be done before capture phase. In other words, changes to the DOM while the event is dispatched <strong>must</strong> not affect the result.
               The same thing also applies to the case when the event dispatching is finished.
               If the event hasn't been dispatched, the attribute <strong>must</strong> create and return a new empty array.
             </p>