The syntax is EXTERNAL(ddname) or EXTERNAL=ddname.
This provides the DDname of the work data set used by the external SORT facility. If not specified, CICS PA assigns an External Work File from a pool of External Work Files with DDnames in the format CPAXWnnn where nnn is a sequential number 001-999 to uniquely identify the work file. There must be one External Work File specified in the JCL for each report that needs one. See External sorting for information on the DD statements for External Work Files.