Tpl::findUsedSourceKeys

public function findUsedSourceKeys($sourceType)
{
	if (!SourceType::isType($sourceType))
	{
		throw new ArgumentException('Incorrect $sourceType', 'sourceType');
	}

	$usages = $this->collectUsages();
	return array_unique(array_column($usages->getBySourceType($sourceType), 1));
}