This interface is to used to every class that loads it self from XML.
In adiction to the isLoadOk() and if the class loads directly
from a file with a XSD you should also implement the following methods:
public static abstract boolean validate(String xml);
public static abstract boolean validate(File file);
This will serve to be called by the load method in order to
validate the XML content again the their schema
(fetch from the ConfigFetch).