IHandler are classes which represent application logic and work
on supplied wrappers to get their data or set default values
which should appear on the html form that is used to supply the
data needed by the handler.
From the application programmers point of view these classes which
handle all the application logic have to be written on their own.
IWrappers are objects which aggregate part of the submitted data
of a HTTP post or get event in a typesafe way and present getter
and setter methods to manipulate that data.
Classes which implement the IWrapper interface are not written by
hand, but are autogenerated from a describtion written in a
special xml format.
From the application programmers point of view IWrappers
are never instanciated directly.