DataProviderManager::getValue

protected function getValue($valueDescription, DataProvider $parentDataProvider = null, $placeholder = null)
{
	$value = false;
	if($parentDataProvider && is_string($valueDescription) && $placeholder !== $valueDescription)
	{
		$value = $parentDataProvider->getValue($valueDescription);
	}
	elseif(is_callable($valueDescription))
	{
		if (
			(
				is_array($valueDescription)
				&& (
					is_a($valueDescription[0], DataProvider::class, true)
					|| is_object($valueDescription[0])
				)
			)
			|| $valueDescription instanceof Closure
		)
		{
			$value = call_user_func($valueDescription, $placeholder);
		}
	}

	return $value;
}