From 7c41fa814fab736ac6e9845ee18e3be6b00f4951 Mon Sep 17 00:00:00 2001
From: Yorick Peterse <yorickpeterse@gmail.com>
Date: Wed, 27 Aug 2014 20:24:40 +0200
Subject: [PATCH] Default attribute namespaces.

When an attribute is prefixed with "xml" the default namespace should be used
automatically. This namespace is not registered on element level by default as
this namespace isn't registered manually, instead it's a "magic" namespace. This
also ensures we match the behaviour of libxml more closely, hopefully reducing
confusion.
---
 lib/oga.rb                     |  2 +-
 lib/oga/xml/attribute.rb       | 21 ++++++++++++++++++++-
 spec/oga/xml/attribute_spec.rb |  6 ++++++
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/lib/oga.rb b/lib/oga.rb
index 5bc0e6a..83537c7 100644
--- a/lib/oga.rb
+++ b/lib/oga.rb
@@ -25,8 +25,8 @@ require_relative 'oga/xml/cdata'
 require_relative 'oga/xml/xml_declaration'
 require_relative 'oga/xml/processing_instruction'
 require_relative 'oga/xml/doctype'
-require_relative 'oga/xml/attribute'
 require_relative 'oga/xml/namespace'
+require_relative 'oga/xml/attribute'
 require_relative 'oga/xml/element'
 require_relative 'oga/xml/node_set'
 
diff --git a/lib/oga/xml/attribute.rb b/lib/oga/xml/attribute.rb
index 1acefb2..7f0c99f 100644
--- a/lib/oga/xml/attribute.rb
+++ b/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  => 'http://www.w3.org/XML/1998/namespace'
+      ).freeze
+
       ##
       # @param [Hash] options
       #
@@ -44,7 +55,15 @@ module Oga
       # @return [Oga::XML::Namespace]
       #
       def namespace
-        return @namespace ||= element.available_namespaces[namespace_name]
+        unless @namespace
+          if namespace_name == DEFAULT_NAMESPACE.name
+            @namespace = DEFAULT_NAMESPACE
+          else
+            @namespace = element.available_namespaces[namespace_name]
+          end
+        end
+
+        return @namespace
       end
 
       ##
diff --git a/spec/oga/xml/attribute_spec.rb b/spec/oga/xml/attribute_spec.rb
index be08cf7..8d9bdb0 100644
--- a/spec/oga/xml/attribute_spec.rb
+++ b/spec/oga/xml/attribute_spec.rb
@@ -24,11 +24,17 @@ describe Oga::XML::Attribute do
         :name           => 'a',
         :element        => element
       )
+
+      @default = described_class.new(:namespace_name => 'xml', :name => 'x')
     end
 
     example 'return a Namespace instance' do
       @attribute.namespace.should == @namespace
     end
+
+    example 'return the default XML namespace when the "xml" prefix is used' do
+      @default.namespace.should == Oga::XML::Attribute::DEFAULT_NAMESPACE
+    end
   end
 
   context '#to_s' do