diff --git a/activesupport/lib/active_support/core_ext/class/subclasses.rb b/activesupport/lib/active_support/core_ext/class/subclasses.rb
index 8a21c71a42cd1372218cf663cc7a3aa4387d25e3..10a7c787f6218c2e1ab479c0dd7b259a65665999 100644
--- a/activesupport/lib/active_support/core_ext/class/subclasses.rb
+++ b/activesupport/lib/active_support/core_ext/class/subclasses.rb
@@ -6,7 +6,20 @@ class Class
     # Test if this Ruby supports each_object against singleton_class
     ObjectSpace.each_object(Numeric.singleton_class) {}
 
-    def descendants # :nodoc:
+    # Returns an array with all classes that are < than its receiver.
+    #
+    #   class C; end
+    #   C.descendants # => []
+    #
+    #   class B < C; end
+    #   C.descendants # => [B]
+    #
+    #   class A < B; end
+    #   C.descendants # => [B, A]
+    #
+    #   class D < C; end
+    #   C.descendants # => [B, A, D]
+    def descendants
       descendants = []
       ObjectSpace.each_object(singleton_class) do |k|
         descendants.unshift k unless k == self
@@ -14,7 +27,7 @@ def descendants # :nodoc:
       descendants
     end
   rescue StandardError # JRuby 9.0.4.0 and earlier
-    def descendants # :nodoc:
+    def descendants
       descendants = []
       ObjectSpace.each_object(Class) do |k|
         descendants.unshift k if k < self