<%-fields_for 'arc[arc_tag_attributes][]', arc_tag do |arc_tag_f|-%>
<p>
  <%= arc_tag_f.label :tag %><br />
  <%= arc_tag_f.text_field :tag_name, :index => nil, :id => '' %>
</p>
  <%-unless arc_tag.new_record?-%>
    <%= arc_tag_f.hidden_field :id, :index => nil, :id => '' %>
  <%-end-%>
<%-end-%>
