WordPress at a glance
action is not described

post_edit_form_tag action-hook . WP 3.0.0

Fires inside the post editor form tag.

Usage

add_action( 'post_edit_form_tag', 'action_function_name_2712' );
function action_function_name_2712( $post ){
	// action...
}
$post(WP_Post)
Post object.

Where the hook is called

In file: /wp-admin/edit-form-advanced.php
post_edit_form_tag
wp-admin/edit-form-advanced.php 384
do_action( 'post_edit_form_tag', $post );

Where the hook is used (in WP core)

Does not used.