my $self = shift;
    $self->run_modes(

        # default
        'index' => 'index',

        # user's tag cloud
        'tag_cloud' => 'tag_cloud',
        'edit_tags' => 'edit_tags',
        'tag_find'  => 'tag_find',

        ..
        # called on unknown mode.
        'AUTOLOAD' => 'unknown_mode',
    );