Documentation: Clarify that runtime.sendMessage does not notify itself

extensions/common/api/runtime.json

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Note: Many of these functions and events are implemented by hand and should
 // not elicit any code generation from the schema compiler. These items are
 // marked "nocompile."
 [
   {
     "namespace": "runtime",
@@ skipping 308 matching lines @@
         "returns": {
           "$ref": "Port",
           "description": "Port through which messages can be sent and received with the application"
         }
       },
       {
         "name": "sendMessage",
         "type": "function",
         "nocompile": true,
         "allowAmbiguousOptionalArguments": true,
-        "description": "Sends a single message to event listeners within your extension/app or a different extension/app. Similar to $(ref:runtime.connect) but only sends a single message, with an optional response. If sending to your extension, the $(ref:runtime.onMessage) event will be fired in each page, or $(ref:runtime.onMessageExternal), if a different extension. Note that extensions cannot send messages to content scripts using this method. To send messages to content scripts, use $(ref:tabs.sendMessage).",
+        "description": "Sends a single message to event listeners within your extension/app or a different extension/app. Similar to $(ref:runtime.connect) but only sends a single message, with an optional response. If sending to your extension, the $(ref:runtime.onMessage) event will be fired in every frame of your extension (except for the sender's frame), or $(ref:runtime.onMessageExternal), if a different extension. Note that extensions cannot send messages to content scripts using this method. To send messages to content scripts, use $(ref:tabs.sendMessage).",
         "parameters": [
           {"type": "string", "name": "extensionId", "optional": true, "description": "The ID of the extension/app to send the message to. If omitted, the message will be sent to your own extension/app. Required if sending messages from a web page for <a href=\"manifest/externally_connectable.html\">web messaging</a>."},
           { "type": "any", "name": "message", "description": "The message to send. This message should be a JSON-ifiable object." },
           {
             "type": "object",
             "name": "options",
             "properties": {
               "includeTlsChannelId": { "type": "boolean", "optional": true, "description": "Whether the TLS channel ID will be passed into onMessageExternal for processes that are listening for the connection event." }
             },
             "optional": true
@@ skipping 221 matching lines @@
           {
             "$ref": "OnRestartRequiredReason",
             "name": "reason",
             "description": "The reason that the event is being dispatched."
           }
         ]
       }
     ]
   }
 ]