Used only in the case of a derived variable, this element provides both a description of how the derivation was performed and the command used to generate the derived variable, as well as a specification of the other variables in the study used to generate the derivation. Alternatively the variables may be expressed as a range using the varRange element. Note that use of varRange is implementation dependent. Since the order of variables can change during the execution of a script, it is computationally difficult to identify which variables belong to a variable range. It has been provided to support the automated creation of derivation information. Order should be determined by the physical order expressed in location as opposed to the order expressed in the metadata document. varRange should only be used when the physical order of variables is available and machine-actionable.