palette/views/jst/conversations/SubmissionCommentFormDialog.handlebars

<form class="reply_form" method="post"
  action="/api/v1/courses/{{conversation.assignment.course_id}}/assignments/{{conversation.assignment_id}}/submissions/{{conversation.user_id}}" class="form-horizontal"
  >

  <input type="hidden" name="_method" value="put">

  <div class='message-body'>
    <textarea name="comment[text_comment]"
              data-track-category="Compose Message"
              data-track-action="Edit"
              data-track-label="Body"
              aria-label="{{#t "body"}}Body{{/t}}"
              class="reply_body"></textarea>
    <div class='context_messages'></div>
  </div>
</form>