diff --git a/.document b/.document
new file mode 100644
index 0000000..48aceb6
--- /dev/null
+++ b/.document
@@ -0,0 +1,4 @@
+LICENSE.txt
+README.md
+docs/
+lib/
diff --git a/docs/random.rb b/docs/random.rb
new file mode 100644
index 0000000..5b7f5dd
--- /dev/null
+++ b/docs/random.rb
@@ -0,0 +1,10 @@
+# This file is only for RDoc
+
+# Random provides an interface to Ruby's pseudo-random number generator, or
+# PRNG.
+#
+# See also Random::Formatter module that adds convenience methods to generate
+# various forms of random data.
+
+class Random
+end
diff --git a/lib/random/formatter.rb b/lib/random/formatter.rb
index e7ee4db..befa1d0 100644
--- a/lib/random/formatter.rb
+++ b/lib/random/formatter.rb
@@ -292,6 +292,7 @@ def uuid_v7(extra_timestamp_bits: 0)
     end
   end
 
+  # Internal interface to Random; Generate random data _n_ bytes.
   private def gen_random(n)
     self.bytes(n)
   end
@@ -339,7 +340,9 @@ def uuid_v7(extra_timestamp_bits: 0)
     result
   end
 
+  # The default character list for #alphanumeric.
   ALPHANUMERIC = [*'A'..'Z', *'a'..'z', *'0'..'9']
+
   # Generate a random alphanumeric string.
   #
   # The argument _n_ specifies the length, in characters, of the alphanumeric
diff --git a/lib/securerandom.rb b/lib/securerandom.rb
index 9afd8a0..43732a6 100644
--- a/lib/securerandom.rb
+++ b/lib/securerandom.rb
@@ -40,19 +40,27 @@
 
 module SecureRandom
 
+  # The version
   VERSION = "0.3.0"
 
   class << self
+    # Returns a random binary string containing +size+ bytes.
+    #
+    # See Random.bytes
     def bytes(n)
       return gen_random(n)
     end
 
     private
 
+    # :stopdoc:
+
+    # Implementation using OpenSSL
     def gen_random_openssl(n)
       return OpenSSL::Random.random_bytes(n)
     end
 
+    # Implementation using system random device
     def gen_random_urandom(n)
       ret = Random.urandom(n)
       unless ret
@@ -78,6 +86,9 @@ def gen_random_urandom(n)
       end
     end
 
+    # :startdoc:
+
+    # Generate random data bytes for Random::Formatter
     public :gen_random
   end
 end