The DatarecordExtension class is a special type of Datarecord which allow the user (or the software) to dynamically change the fields of the object.
If the Datarecord represents a car in a car database, the DatarecordExtension allows the user to customize the object with her own fields such as license plate number or color.
The class works just like a normal Datarecord except that one can call:
DatarecordExtensiblefield::renderEditComplexForClass('Myclass');
to present an interface for adding and removing fields from this class.