Language codes are closely related to the localising process because they indicate the locales involved in the translation and adaptation of the product. They are used in various contexts; for example, they might be informally used in a document published by the European Union or they might be introduced in HTML element under the attribute. In the case of the European Union style guide, the language codes are based on the ISO 639-1 alpha-2 code; in HTML, the language tags are generally defined within the Internet Engineering Task Force's "Best Current Practice" (BCP) 47. The decision to use one type of code or tag versus another depends upon the nature of the project and any requirements set out for the localisation specialist.