The PEAR Installer classes provides an API for
  the administration and management
  of PEAR Packages.
 
 This class is for objects where you want to separate the code for  
 some methods into separate classes.  This is useful if you have a  
 class with not-frequently-used methods that contain lots of code  
 that you would like to avoid always parsing.
 Class Trees for PEAR_Autoloader