phpDocumentor如何记录字符串参数的可用选项

/**
* Set size of photos
* 
* @param string $size can be one of these options: url_sq, url_t, url_s, url_m, url_o
* @return void
*/
public function setSize($size){
    $this->_size = $size;
}

class TheClass
{
 const photo_size_sq = \'url_sq\';
 const photo_size_tiny = \'url_t\';
 const photo_size_small = \'url_s\';
 const photo_size_m = \'url_m\';
 const photo_size_o = \'url_o\';

/**
* Set size of photos
* 
* @param string $size see photo_size_* constants
* @return void
*/
public function setSize($size){
    $this->_size = $size;
}
}

$object->setSize($object::photo_size_small);