hook_comment form operation is no longer working in D6

http://api.drupal.org/api/function/hook_comment/6

According to the above documentation, it still says there is a "form" action in which the "comment form is about to be shown. Modules may add fields to the form at this point."

I have a D5 module using this particular action to add fields to my comment form but this is no longer working in D6. If the way the comment form is rendered has changed and this action is no longer working, shouldn't the documentation be updated with an alternative to the deprecated action?