This standard defines the structure of a register of essence element keys as used by essence container specifications coded according to SMPTE ST 336, e.g. SMPTE ST 379-1 and ST 379-2 and related Essence Mapping Documents. The standard normatively defines universal identifiers, essence element names, definitions, and standardized symbols, as well as other normative and informative fields. - The associated essence element key register includes all entries which have been approved according to the specific procedures defined in SMPTE AG 18.