Indicates the user-defined element type of the UnmanagedType.SafeArray.
Initialize this field with your custom type to enable the elements of the SAFEARRAY to be marshaled successfully. This field is only needed when the MarshalAsAttribute.SafeArraySubType is either VarEnum.VT_UNKNOWN, VarEnum.VT_DISPATCH, or VarEnum.VT_RECORD. For additional information, see [<topic://cpcondefaultmarshalingforarrays>].