Document identifier format is a controlled vocabulary that describes the standardised syntax of the identifiers of documents produced by the institutions of the European Union in particular. It was created to be used by metadata in the AKN4EU mark-up language. It provides for each identifier marked a mapping with a standardised syntax with a decomposition into the subcomponents and for each subcomponent a meaning depending on the type of identifier. Each institution can have its own naming convention and is allowed to map it according to its own naming convention inside the text. Document identifier format is maintained by the Publications Office of the European Union on EU Vocabularies website.