protected function _store($domain, $header, $sentence)
{
if (!isset($this->_storage[$domain])) {
$this->_storage[$domain] = [];
}
if (!isset($this->_storage[$domain][$sentence])) {
$this->_storage[$domain][$sentence] = $header;
} else {
$this->_storage[$domain][$sentence] .= $header;
}
}