C++ get pointer safety

I was reading thru this code about pointer safety but could not understand that different values and its meaning?

value   description
relaxed The validity of a pointer value does not depend on whether it is a 
        safely-derived pointer value.
preferred   The validity of a pointer value does not depend on whether it is 
            a safely-derived pointer value. A leak detector may be running
            so that the program can avoid spurious leak reports.
strict  A pointer value that is not a safely-derived pointer value is an 
        invalid pointer value (unless the referenced complete object is of 
        dynamic storage duration and has previously been declared reachable).    
        A garbage collector may be running so that non-traceable object are 
        automatically deleted.

Is there any example or document that explains about it?