The format of the platform string must be OS-version-cpu-extra if any more specific information is needed, and the OS must be in lower case as in "windows." The match is performed using a regular expression, but uses * and ? wildcards instead of .* and .?. Note that hpux/aix/irix/linux are all exclusive. To select non-windows, use an expression like (*ix|*ux|darwin). If using PEAR 1.3.2 and newer, use !windows.
This information is based on eyeing the source for OS/Guess.php, so if you are unsure of what to do, read that file.
relative path of file (relative to packagedirectory option)
platform descriptor string