register_post_type & 'register_meta_box_cb' argument

Question

I just tried the first time to extend a custom post type admin-UI-edit-page with some "meta" boxes (if this is the right word).

register_post_type('post_type', array('register_meta_box_cb' => 'additional_input_field') );

function additional_input_field() {
global $post;
$custom = get_post_custom( $post->ID );
$length = $custom["post_type-length"][0];

return print '<label>Length:</label><input name="post_type-length" value="'.$length.'" />'; }

So far i haven't seen any documentation or example about how to use this. A look in the core showed me that it should be equal to:

add_action( 'add_meta_boxes'.$post_type, 'additional_input_field', 10, 1 );

The appropriate hook can be found in (core) /root/wp-admin/edit-form-advanced.php line 163. The call for add_action in (core) /root/wp-includes/post.php line 877. The only problem is that it doesn't seem to work as expected. The field get's loaded in front (visually: on top) of everything else. If i try to hook it directly to 'add_meta_boxes'.$post_type, i get nothing...

Simplified examples in this text to show what i mean. Typos may be there but doesn't matter. The callback fn is taken from some sample code over here.

Answer 1

I love answering my own questions: Wrap the function add_additional_input_field() in a new function that contains this and call it in the register_meta_box_cb argument.

And yes: This is the solution.