Distinguish default attribute/element namespaces

The previous commit messed this up because I wasn't fully awake.

lib/oga/xml/attribute.rb

@@ -21,6 +21,17 @@ module Oga
     class Attribute
       attr_accessor :name, :namespace_name, :element, :value
 
+      ##
+      # The default namespace available to all attributes. This namespace can
+      # not be modified.
+      #
+      # @return [Oga::XML::Namespace]
+      #
+      DEFAULT_NAMESPACE = Namespace.new(
+        :name => 'xml',
+        :uri  => XML::DEFAULT_NAMESPACE.uri
+      ).freeze
+
       ##
       # @param [Hash] options
       #

lib/oga/xml/default_namespace.rb

@@ -6,7 +6,7 @@ module Oga
     # @return [Oga::XML::Namespace]
     #
     DEFAULT_NAMESPACE = Namespace.new(
-      :name => 'xml',
+      :name => 'xmlns',
       :uri  => 'http://www.w3.org/XML/1998/namespace'
     ).freeze
   end # XML

spec/oga/xml/attribute_spec.rb

@@ -33,7 +33,7 @@ describe Oga::XML::Attribute do
     end
 
     it 'returns the default XML namespace when the "xml" prefix is used' do
-      @default.namespace.should == Oga::XML::DEFAULT_NAMESPACE
+      @default.namespace.should == Oga::XML::Attribute::DEFAULT_NAMESPACE
     end
   end