Transforms stored field values into the format the widgets need.
function _options_storage_to_form($items, $options, $column, $properties) {
$items_transposed = options_array_transpose($items);
$values = isset($items_transposed[$column]) && is_array($items_transposed[$column]) ? $items_transposed[$column] : array();
// Discard values that are not in the current list of options. Flatten the
// array if needed.
if ($properties['optgroups']) {
$options = options_array_flatten($options);
}
$values = array_values(array_intersect($values, array_keys($options)));
return $values;
}