app/views/articles/form/_content.html.erb
<div class="row">
<%= form_for article, validate: true, html: { class: "dbl-col" } do |f| %>
<fieldset>
<div id='article-sections'>
<%= f.fields_for :article_sections do |file| %>
<%= render 'articles/form/article_section_fields', f: file %>
<% end %>
<div class='links'>
<%= link_to_add_association '+ Add Section', f, :article_sections,
html_options = { partial: 'articles/form/article_section_fields' } %>
</div>
</div>
<%= render partial: 'articles/form/submit_buttons', locals: { f: f } %>
</fieldset>
<% end %>
</div>