my ($optgroup_title, $sub_collection) = @{ $_ };
$self->html_tag('optgroup', $list_to_code->($sub_collection), label => $optgroup_title)
} @{ $collection };
my ($optgroup_title, $sub_collection) = @{ $_ };
$self->html_tag('optgroup', $list_to_code->($sub_collection), label => $optgroup_title)
} @{ $collection };