protected function isValid($value)
{
$parser = new EelParser($value);
$result = $parser->match_Expression();
if ($result === false) {
$this->addError('Expression "%s" could not be parsed.', 1421940748, [$value]);
} elseif ($parser->pos !== strlen($value)) {
$this->addError('Expression "%s" could not be parsed. Error starting at character %d: "%s".', 1421940760, [$value, $parser->pos, substr($value, $parser->pos)]);
}
}