Enable to omit ConversionException during unmarshalling

Implement a method of com.thoughtworks.xstream.XStream for setting some property that enables to ignore any extra incoming xml elements, not present in the mapping bean and not aliased.

For instance:

public class LetterHolder {
  private String A;
  private String B;

  // getters and setters ...
}

<LetterHolder>
<A>This is letter A</A>
<B>B</B>
<C>C</C>
</LetterHolder>

After setting this new property calling of XStream#unmarshal(...) will not throw com.thoughtworks.xstream.converters.ConversionException: C : C : C : C.