How eZ Tags adds tags

addTag.php

function add($parentTag, $newKeyword)
{
    $db = eZDB::instance();
    $db->begin();

    $tag = new eZTagsObject( array( 'parent_id'   => ( $parentTag instanceof eZTagsObject ) ? $parentTag->attribute( 'id' ) : 0,
                                    'main_tag_id' => 0,
                                    'keyword'     => $newKeyword,
                                    'depth'       => ( $parentTag instanceof eZTagsObject ) ? (int) $parentTag->attribute( 'depth' ) + 1 : 1,
                                    'path_string' => ( $parentTag instanceof eZTagsObject ) ? $parentTag->attribute( 'path_string' ) : '/' ) );

    $tag->store();
    $tag->setAttribute( 'path_string', $tag->attribute( 'path_string' ) . $tag->attribute( 'id' ) . '/' );
    $tag->store();
    $tag->updateModified();

    /* Extended Hook */
    if ( class_exists( 'ezpEvent', false ) )
        ezpEvent::getInstance()->filter( 'tag/add', array( 'tag' => $tag, 'parentTag' => $parentTag ) );

    $db->commit();

    return $Module->redirectToView( 'id', array( $tag->attribute( 'id' ) ) );
}