Class::Data::Inheritable is for creating accessor/mutators to class data.
That is, if you want to store something about your class as a whole
(instead of about a single object). This data is then inherited by your
subclasses and can be overriden.

For example:

Pere::Ubu->mk_classdata('Suitcase');

will generate the method Suitcase() in the class Pere::Ubu.

This new method can be used to get and set a piece of class data.

Pere::Ubu->Suitcase('Red');
$suitcase = Pere::Ubu->Suitcase;

The interesting part happens when a class inherits from Pere::Ubu:

package Raygun;
use base qw(Pere::Ubu);

# Raygun's suitcase is Red.
$suitcase = Raygun->Suitcase;

Raygun inherits its Suitcase class data from Pere::Ubu.

Inheritance of class data works analogous to method inheritance. As long as
Raygun does not "override" its inherited class data (by using Suitcase() to
set a new value) it will continue to use whatever is set in Pere::Ubu and
inherit further changes:

# Both Raygun's and Pere::Ubu's suitcases are now Blue
Pere::Ubu->Suitcase('Blue');

However, should Raygun decide to set its own Suitcase() it has now
"overridden" Pere::Ubu and is on its own, just like if it had overriden a
method:

# Raygun has an orange suitcase, Pere::Ubu's is still Blue.
Raygun->Suitcase('Orange');

Now that Raygun has overridden Pere::Ubu futher changes by Pere::Ubu no
longer effect Raygun.

# Raygun still has an orange suitcase, but Pere::Ubu is using Samsonite.
Pere::Ubu->Suitcase('Samsonite');