How should I include files from outside of document root?

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http://stackoverflow.com – I wanted to include pear/Mail.php. I asked the hosting support to provide me the path, It is "/usr/local/php-5.3.17/share/pear/". But it doesn't work from document root, and it seems I can't access upper level directories by using "../". There are two parent folder for the document root: /home/www/ (HowTos)