ISO 19160-4:2017 defines key terms for postal addressing, postal address components and constraints on their use. Specifically, ISO 19160-4:2017 defines postal address components organized into three hierarchical levels: - elements, such as organization name or postcode, which have well-defined conceptual meaning and are not themselves made up of subordinate components, though they may be sub-divided for technical purposes; - constructs, such as organization identification, which group elements into units form a logical portion of a postal address; - segments, such as addressee specification, which group-related postal address constructs and/or postal address elements into units with a specific defined function. ISO 19160-4:2017 also specifies a mechanism for creation of sub-elements, which correspond to either sub-divisions of element content, such as door type or door indicator or to multiple occurrences and locations of elements in an address, such as levels of administrative regions. ISO 19160-4:2017 does not specify the length of any component nor the value range of any component. Moreover, ISO 19160-4:2017 defines the codes to identify elements and sub-elements. Further, ISO 19160-4:2017 specifies postal address rendering rules. This includes identification and ordering of output lines in a rendered address, conditions for selection of candidate lines, the order and concatenation of postal address components, required and optional components, parameters to contextualize address for rendering and the formatting of the components, subject to constraints on the space available for that task. Postal address rendering rules are represented in ISO 19160-4:2017 as a postal address template. Finally, ISO 19160-4:2017 specifies language suitable for computer processing to formally express postal address templates.