@headers["Content-Type"] = "text/xml; charset=utf-8"
xml.todos_by_context do
   @contexts_to_show.each do |c|
      xml.context do 
        xml.name c.name
        xml.hide c.hide, :type => :boolean
        xml.id c.id, :type => :integer
        xml.position c.position, :type => :integer
        c.not_done_todos.each do |t|
          xml << t.to_xml( :skip_instruct => true, :root => 'todo', :except => [:user_id, :context_id] )
        end
      end
    end
end