simple PHP class

[eluser]Ajaxian64[/eluser]
Hi,

I would like to set up a php class. Problem, is that it is not a helper and not a library.
For instance a simple class that aims to provide msg status and text about problem whenever status is ko.
It is just an example.

How can I handle this with CI ?
Where can I declare my class Mess { } ? In library folder ?
I don't know wher I have to declare of my class in order I can make a new Msg() in different parts of my CI appclication (models, controller)

I hope I am clear enough ...

Thanks