prototype link_to_function

hi everybody! i`m trying to apply this function(prototype):
<%= link_to_function "reply", "$('main-comment-form')
.hide()
.appendTo('comment-#{comment.id} .form-placeholder') //problem is here
probably
.fadeToggle(600);
$('comment_parent_id').setValue(#{comment.id});"%>

after clicking the link form hides succesfully, but it doesn`t append to
.form-placeholder

<div id="comment-6">
  <span id="commenter">July</span><span id="comment-date">
    (September 23, 2009 at 11:15 PM)</span><br>

  stupid ukrainians!!
  <div class="form-placeholder"></div>
</div>

how do we specify id and class to append the form using prototype?