ISO/IEC 21000-20:2016 specifies a language for representing contracts in the Multimedia Framework formed for the transaction of MPEG-21 Digital Items or services related to the MPEG-21 Framework.

Contract Expression Language (CEL) aims at digitally representing the agreements made in environments using ISO/IEC 21000. These agreements are contracts for transactions of content packed as Digital Items, as well as services provided around this content.

The range of contracts under scope are as follows:

- contracts about transactions on rights for the exploitation of content as MPEG-21 Digital Items;

- contracts about the provision of MPEG-21-based services, i.e. delivery, identification, encryption, search and others.

The aspects represented by CEL contracts include the following:

- the textual clauses, in natural language as they are in the narrative contract, duly structured;

- the operative clauses, as computer language expressions.