A method of operating a system including a digital network interconnected intelligent digital devices (IDDS) generating and receiving eXtensible Markup Language (XML) documents containing data and respective Document Type Definitions (DTDs) describing the data content. Preferably, the method includes steps for transmitting a generated XML document from a first IDD to a second IDD, and, when the respective DTD for the generated XML document satisfies a predetermined criteria, operating on the data contained in the XML document at the second IDD. In a first exemplary case, the second IDD maintains a list of trusted DTDs, and the predetermined criteria is equality between the name of the respective DTD and the name of a trusted DTD. Alternatively, the predetermined criteria is satisfied by inclusion of the name of a program residing on the second IDD in the respective DTD. In a second exemplary case, the transmitting step includes transmitting the generated XML document from the first IDD to the second IDD and a third IDD, the operating step includes operating on the data contained in the XML document at the second IDD when the respective DTD for the generated XML document satisfies a first predetermined criteria, and the method further includes the step of operating on the data contained in the XML document at the third IDD when the respective DTD for the generated XML document satisfies a second predetermined criteria. A system composed of IDDs interconnected by an in home digital network (IHDN) or other mechanism, which system can be operated by the method mentioned above, is also described.