public function vary($cacheVariances = null)
{
if ($cacheVariances !== null) {
$cacheVariances = (array) $cacheVariances;
$this->_headers['Vary'] = implode(', ', $cacheVariances);
}
if (isset($this->_headers['Vary'])) {
return explode(', ', $this->_headers['Vary']);
}
return null;
}