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Further to Volka's answer and relating to finding out even more information about how PHP is setup...
If you want to find out information like this on your own installation of PHP do a search in your files and have a look at your php.ini file. Alternatively you could try putting
into a file and running it. That'll tell you everything you need to know about how PHP is configured and what's been enabled and what hasn't (and you can look at this even if you don't have access to the php.ini file, if for example you want to look at your host's PHP config).