diff --git a/mrbgems/mruby-enum-chain/mrblib/chain.rb b/mrbgems/mruby-enum-chain/mrblib/chain.rb
index 43d0926c8..fb0dac66b 100644
--- a/mrbgems/mruby-enum-chain/mrblib/chain.rb
+++ b/mrbgems/mruby-enum-chain/mrblib/chain.rb
@@ -3,12 +3,33 @@
 # See Copyright Notice in mruby.h
 
 module Enumerable
+  #
+  # call-seq:
+  #   enum.chain(*enums) -> enumerator_chain
+  #
+  # Returns an Enumerator::Chain object which can enumerate over this
+  # enumerable and the given enumerables in sequence.
+  #
+  #   e = (1..3).chain([4, 5])
+  #   e.to_a  #=> [1, 2, 3, 4, 5]
+  #
   def chain(*args)
     Enumerator::Chain.new(self, *args)
   end
 end
 
 class Enumerator
+  #
+  # call-seq:
+  #   enum + other_enum -> enumerator_chain
+  #
+  # Returns an Enumerator::Chain object which can enumerate over this
+  # enumerator and the given enumerator in sequence.
+  #
+  #   e1 = (1..3).each
+  #   e2 = [4, 5].each
+  #   (e1 + e2).to_a  #=> [1, 2, 3, 4, 5]
+  #
   def +(other)
     Chain.new(self, other)
   end
@@ -16,11 +37,34 @@ class Enumerator
   class Chain
     include Enumerable
 
+    #
+    # call-seq:
+    #   Enumerator::Chain.new(*enums) -> enumerator_chain
+    #
+    # Generates a new enumerator which iterates over each one of the
+    # given enumerable objects in sequence.
+    #
+    #   e = Enumerator::Chain.new(1..3, [4, 5])
+    #   e.to_a  #=> [1, 2, 3, 4, 5]
+    #
     def initialize(*args)
       @enums = args.freeze
       @pos = -1
     end
 
+    #
+    # call-seq:
+    #   chain.each { |obj| block } -> chain
+    #   chain.each                 -> enumerator
+    #
+    # Iterates over the elements of the first enumerable by calling the
+    # each method on it with the given block, then proceeds to the next
+    # enumerable in the chain and continues until the end.
+    #
+    #   e = Enumerator::Chain.new(1..3, [4, 5])
+    #   e.each { |x| puts x }
+    #   # prints: 1, 2, 3, 4, 5
+    #
     def each(&block)
       return to_enum unless block
 
@@ -34,6 +78,16 @@ class Enumerator
       self
     end
 
+    #
+    # call-seq:
+    #   chain.size -> integer or nil
+    #
+    # Returns the total size of the enumerator chain if all of the
+    # chained enumerables define size. Otherwise it returns nil.
+    #
+    #   Enumerator::Chain.new(1..3, [4, 5]).size  #=> 5
+    #   Enumerator::Chain.new(1..3, loop).size    #=> nil
+    #
     def size
       @enums.reduce(0) do |a, e|
         return nil unless e.respond_to?(:size)
@@ -41,6 +95,19 @@ class Enumerator
       end
     end
 
+    #
+    # call-seq:
+    #   chain.rewind -> chain
+    #
+    # Rewinds the enumerator chain by calling the rewind method on each
+    # enumerable that has been iterated, in reverse order. Each enumerable
+    # that defines a rewind method will be rewound.
+    #
+    #   e = Enumerator::Chain.new((1..3), [4, 5])
+    #   e.next  #=> 1
+    #   e.rewind
+    #   e.next  #=> 1
+    #
     def rewind
       while 0 <= @pos && @pos < @enums.size
         e = @enums[@pos]
@@ -51,10 +118,30 @@ class Enumerator
       self
     end
 
+    #
+    # call-seq:
+    #   chain + other_enum -> enumerator_chain
+    #
+    # Returns a new Enumerator::Chain object which will enumerate over the
+    # elements of this chain, followed by the elements of other_enum.
+    #
+    #   e1 = Enumerator::Chain.new(1..3, [4, 5])
+    #   e2 = e1 + [6, 7]
+    #   e2.to_a  #=> [1, 2, 3, 4, 5, 6, 7]
+    #
     def +(other)
       self.class.new(self, other)
     end
 
+    #
+    # call-seq:
+    #   chain.inspect -> string
+    #
+    # Returns a printable version of the enumerator chain.
+    #
+    #   Enumerator::Chain.new(1..3, [4, 5]).inspect
+    #   #=> "#<Enumerator::Chain: [1..3, [4, 5]]>"
+    #
     def inspect
       "#<#{self.class}: #{@enums.inspect}>"
     end