<%= nested_form_for Project.new do |f| -%>
  <%= f.fields_for :tasks do |tf| -%>
    <%= tf.fields_for :milestones do |mf| %>
      <%= mf.text_field :name %>
      <%= mf.link_to_remove 'Remove milestone' %>
    <% end %>
    <%= tf.link_to_add 'Add new milestone', :milestones %>
    <%= tf.link_to_remove 'Remove' %>
  <% end -%>
  <%= f.link_to_add 'Add new task', :tasks %>
<% end -%>
