Prevent reserved beacons from being sent manually. (#134)

spec.bs

@@ -763,7 +763,7 @@ following [=struct/items=]:
   :: a [=boolean=], initially false
 </dl>
 
-An <dfn for=fencedframetype>automatic beacon event type</dfn> is either "<dfn
+An <dfn export for=fencedframetype>automatic beacon event type</dfn> is either "<dfn
 for="automatic beacon event type">`reserved.top_navigation_start`</dfn>", "<dfn
 for="automatic beacon event type">`reserved.top_navigation_commit`</dfn>", or "<dfn
 for="automatic beacon event type">`reserved.top_navigation`</dfn>".
@@ -1008,6 +1008,8 @@ A <dfn for=fencedframetype>destination event</dfn> is either a
   In order to <dfn>report a private aggregation event</dfn> using a [=fencedframetype/fenced frame
   reporter=] |reporter| with a [=string=] |event|, run these steps:
 
+  1. If |event|'s {{FenceEvent/eventType}} [=string/starts with=] "`reserved.`", then return.
+
   1. |reporter| |event| <span class=XXX>TODO: Fill this in</span>
 </div>
 
@@ -1522,6 +1524,8 @@ Several APIs specific to fenced frames are defined on the {{Fence}} interface.
 
   1. If |event| is a {{FenceEvent}}:
 
+     1. If |event|'s {{FenceEvent/eventType}} [=string/starts with=] "`reserved.`", then return.
+
      1. If |event| has a {{FenceEvent/destinationURL}}:
         1. If |event| has a {{FenceEvent/destination}} or a {{FenceEvent/eventType}} or a
            {{FenceEvent/eventData}}: