making variable names a little more clear

activesupport/lib/active_support/core_ext/hash/reverse_merge.rb

@@ -21,7 +21,8 @@ class Hash
   # Performs the opposite of <tt>merge</tt>, with the keys and values from the first hash taking precedence over the second.
   # Modifies the receiver in place.
   def reverse_merge!(other_hash)
-    merge!( other_hash ){|k,o,n| o }
+    # right wins if there is no left
+    merge!( other_hash ){|key,left,right| left }
   end
 
   alias_method :reverse_update, :reverse_merge!