Testing extra attachment fields

gistfile1.php

<?php
function add_attachment_location_field( $form_fields, $post ) {
    $field_value = get_post_meta( $post->ID, 'location', true );
    $form_fields['location'] = array(
        'value' => $field_value ? $field_value : '',
        'label' => __( 'Location' ),
        'helps' => __( 'Set a location for this attachment' )
    );
    return $form_fields;
}
add_filter( 'attachment_fields_to_edit', 'add_attachment_location_field', 10, 2 );

function save_attachment_location( $attachment_id ) {
    if ( isset( $_REQUEST['attachments'][$attachment_id]['location'] ) ) {
        $location = $_REQUEST['attachments'][$attachment_id]['location'];
        update_post_meta( $attachment_id, 'location', $location );
    }
}
add_action( 'edit_attachment', 'save_attachment_location' );