Creating custom meta tags by creating new .inc file

In this thread, http://drupal.org/node/296963, i have explain how i've created a new meta tag from .inc file
I put this with a more explicit subject because it could be usefull :
1 - i've made a copy of the file metatags/description.inc
2 - i've rename the copy of : metatags/subect.inc
3 - i've rename the functions :
- nodewords_description_prepare => nodewords_subject_prepare
- nodewords_description_form => nodewords_subject_form
and the line :
- '#title' => t('Description') => '#title' => t('Subject')
saving, and it works fine.

Here is the file attached... (
Now, i'd like to add a DC.subject meta tag, but it doesn't work : I don't know where the Name argument is defined ?