Doctrine\Cache\Cache\AbstractCache::deleteByPrefix() vs. cache namespace

The methods deleteByPrefix() / deleteByRegExp() / deleteBySuffix() are based on the method getIds(), which returns unique identifiers with an added namespace in the front. That is why to be able to delete cells using these three methods, you have to know the namespace.
Example:

$cacheDriver->setNamespace('ns');
$cacheDriver->save('data', 'name');
$cacheDriver->deleteByPrefix('data');

In this example the cell will not be deleted.