[drupal-support] Locking comment subject to the node title

[Abalieno]

I made a little step forward on my own:
  $form .= form_textfield(t('Subject'), 'subject', $edit['subject'] ? 
$edit['subject'] : 'Re: '. $node->title, 60, 64);

This correctly displays "Re:"
But it seems that the function isn't aware of the node array. Can someone 
help how to import it so I can input the title on that line?

The syntax seems correct but the form shows nothing because I believe the 
definition of the node is external.