tracks/app/views/todos/_toggle_successors.html.erb

<%= link_to(image_tag( 'blank.png', :width=>'16', :height=>'16', :border=>'0' ), "#", {:class => 'show_successors', :title => 'Show successors'}) %>

<div class="todo_successors" id="<%= dom_id(item, 'successors') %>">
  <%= render :partial => "todos/successor",
             :collection => item.pending_successors,
             :locals => { :todo => item,
                          :parent_container_type => parent_container_type, 
                          :suppress_dependencies => true,
                          :predecessor => item }
  %>
</div>