The International Standard has been developed to assist developers and users of intelligent transport systems (ITS) standards who wish to use extensible markup language (XML), by providing a consistent definition of the rules and rule references for the use of XML within ITS systems. The scope of the International Standard is to define consistent rules and rule references to provide a framework to be used when implementing XML-based applications in ITS, and particularly, in specifying XML in ITS standards, ITS data registries and ITS data dictionaries. This International Standard also provides guidance and examples in respect of the use of XML in ITS, and the elaboration of XML within the abstract syntax notation one (ASN.1) data definitions required by ISO 14813-6 and ISO 14817.