--- a/toolkit/components/telemetry/docs/core-ping.rst
+++ b/toolkit/components/telemetry/docs/core-ping.rst
@@ -20,33 +20,65 @@ Submission will be per the Edge server s
 * ``appBuildID`` is the build number
 
 Note: Counts below (e.g. search & usage times) are “since the last
 ping”, not total for the whole application lifetime.
 
 Structure::
 
     {
-      "v": 1, // ping format version
+      "v": 2, // ping format version
       "clientId": <string>, // client id, e.g.
                             // "c641eacf-c30c-4171-b403-f077724e848a"
       "seq": <positive integer>, // running ping counter, e.g. 3
       "locale": <string>, // application locale, e.g. "en-US"
       "os": <string>, // OS name.
       "osversion": <string>, // OS version.
       "device": <string>, // Build.MANUFACTURER + " - " + Build.MODEL
                           // where manufacturer is truncated to 12 characters
                           // & model is truncated to 19 characters
       "arch": <string>, // e.g. "arm", "x86"
       "profileDate": <pos integer>, // Profile creation date in days since
                                     // UNIX epoch.
+      "defaultSearch": <string>, // Identifier of the default search engine,
+                                 // e.g. "yahoo".
 
       "experiments": [<string>, …], // Optional, array of identifiers
                                     // for the active experiments
     }
 
+Field details
+-------------
+
+device
+~~~~~~
 The ``device`` field is filled in with information specified by the hardware
 manufacturer. As such, it could be excessively long and use excessive amounts
 of limited user data. To avoid this, we limit the length of the field. We're
 more likely have collisions for models within a manufacturer (e.g. "Galaxy S5"
 vs. "Galaxy Note") than we are for shortened manufacturer names so we provide
 more characters for the model than the manufacturer.
 
+defaultSearch
+~~~~~~~~~~~~~
+On Android, this field may be ``null``. To get the engine, we rely on
+``SearchEngineManager#getDefaultEngine``, which searches in several places in
+order to find the search engine identifier:
+
+* Shared Preferences
+* The distribution (if it exists)
+* The localized default engine
+
+If the identifier could not be retrieved, this field is ``null``. If the
+identifier is retrieved, we attempt to create an instance of the search
+engine from the search plugins (in order):
+
+* In the distribution
+* From the localized plugins shipped with the browser
+* The third-party plugins that are installed in the profile directory
+
+If the plugins fail to create a search engine instance, this field is also
+``null``.
+
+Version history
+---------------
+* v2: added ``defaultSearch``
+* v1: initial version