Simple. The PHP Project uses CVS to manage its sources, so to retrieve the sources for the PHP Manual you will checkout (download) these sources from CVS. An anonymous CVS user named cvsread exists (password: phpfi) that anybody in the world may use to make checkouts. For example:
$ cvs -d :pserver:cvsread@cvs.php.net:/repository login $ cvs -d :pserver:cvsread@cvs.php.net:/repository checkout phpdoc
The above assumes you have CVS installed. Odds are if you're using Linux or Mac that this is already installed, but Windows users aren't so lucky (or unlucky, depending on your feelings towards CVS!) The simplest method for Windows users is TortoiseCVS, see the FAQ for that.
There will now exist a directory named phpdoc that houses all sources files for the PHP Manual.
Sure, it's simple and offers a friendly GUI so if you're into that then go for it! And besides, it also installs the cvs command so it may be used in your Terminal too. The steps include: