$conditions parameter in Nette\Caching\Cache::clean

Hi,

there is a description of clean() method in the documentation page. However, I think there are two things that may confuse a beginner.

1. The clean() method allows to pass no argument. What is the method supposed to do in that case?
2. The documentation page does not mention Cache::ALL condition. The Czech documentation page mentions at least that the condition Cache::ALL exists but without an example.

Have a nice day!

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$cache->clean(array(
    Cache::ALL => TRUE
));