Creation of a new DTD for the external subset. To create an
           internal subset, use xmlCreateIntSubset().

def newDtd(self, name, ExternalID, SystemID):
        """Creation of a new DTD for the external subset. To create an
           internal subset, use xmlCreateIntSubset(). """
        ret = libxml2mod.xmlNewDtd(self._o, name, ExternalID, SystemID)
        if ret is None:raise treeError('xmlNewDtd() failed')
        __tmp = xmlDtd(_obj=ret)
        return __tmp