diff --git a/db/nosql/mongo/docs/courses.txt b/db/nosql/mongo/docs/courses.txt
index b6617a69a..1f584cc8c 100644
--- a/db/nosql/mongo/docs/courses.txt
+++ b/db/nosql/mongo/docs/courses.txt
@@ -41,6 +41,30 @@ MongoDB Essentials – Complete MongoDB Guide
     https://www.torrentdownloads.pro/torrent/1668225001/MongoDB-Essentials---Complete-MongoDB-Guide
     magnet:?xt=urn:btih:96F2D7B67D9F591C201CDE479C2159506E7C66E6
     ! 12.2G
+    ! Extended Json - Shell mode, ? strict
+    ! typeof obj.a;
+    ! obj.c instanceof Array;
+    ! BSON type identifiers
+    !   String           2  "string"
+    !   Object           3  "object"
+    !   Array            4  "array"
+    !   Boolean          8  "bool"
+    !   32-bit Integer  16  "int"
+    !   64-bit Integer  18  "long"
+    !   Double           1  "double"
+    !   Date             9  "date"
+    !   ObjectId         7  "objectId"
+    !
+    ! $type - operator in MongoDB to query documents by BSON
+    ! _id - unique id across MongoDB database, mandatory field,
+    !   may be assigned manually
+    ! _id = ObjectId("a8b4..."); // 12-byte
+    !   4 bytes - date in seconds
+    !   3 bytes - unique machine id hash
+    !   2 bytes - process id of mongo
+    !   3 bytes - unique id
+    !
+    ! ISODate("2018-08-08T08:22:55.160Z")
 2019
 Stashchuk - Introduction to the MongoDB
     https://gigacourse.com/introduction-to-the-mongodb/