tracks/app/views/todos/_toggle_notes.rhtml

<%= link_to(image_tag( 'blank.png', :width=>'16', :height=>'16', :border=>'0' ), "#", {:class => 'show_notes', :title => 'Show notes'}) %>
<% apply_behavior 'a.show_notes:click', :prevent_default => true do |page, element|
  element.next('.todo_notes').toggle
end -%>
<div class="todo_notes" id="<%= dom_id(item, 'notes') %>" style="display:none">
  <%= markdown( item.notes.gsub(/((https?:\/\/[^ \n\t]*))/, '"\1":\2') ) %>
</div>