This class allows to register user custom classes for extra dgn element ( type OdDgElement::kTypeExtraGraphicsElement and type OdDgElement::kTypeExtraNonGraphicsElement ) of specific extended element type ( see OdDgExtendedElementTypeXAttribute). The custom element class must be inherited from base proxy class, that corresponded to extra dgn element of the extended type. (OdDgProxyElement, OdDgProxyGraphicsElement or OdDgComplexProxyElement classes ) 

Corresponding C++ library: TD_Gi