More wording tweaks from @annevk feedback

(like the other commits, this will be squashed out of existence before landing).

Author: RByers

dom.bs

@@ -737,7 +737,7 @@ inherits from the {{Event}} interface.
 
  <dt><code><var>event</var> . {{Event/defaultPrevented}}</code>
  <dd>Returns true if
- {{Event/preventDefault()}} was invoked successfully to indicate cancellation.
+ {{Event/preventDefault()}} was invoked successfully to indicate cancellation, and false otherwise.
 
  <dt><code><var>event</var> . {{Event/isTrusted}}</code>
  <dd>Returns true if <var>event</var> was