Object classes allow a series of actions to be performed on a group of package objects at installation or removal. You assign objects to a class in the prototype file. All package objects must be given a class, although the class of none is used by default for objects that require no special action.
The installation parameter
CLASSES, defined in the pkginfo file, is a list of classes to be installed (including the none class).
CLASSES list determines the order of installation. Class none is always installed first, if present, and removed last. Since directories are the fundamental support structure for all other file system objects, they should all be assigned to the none class. Exceptions can be made, but as a general rule, the none class is safest. The reason for this is to ensure that the directories are created before the objects they will contain and also to ensure that no attempt is made to delete a directory before it has been emptied.