Character

You can use SET INDEX, SET ORDER, and USE to specify which .idx index file or .cdx compound index tag is the master controlling index file or tag. For more information on specifying a master controlling index or tag, see SET INDEX, SET ORDER, and USE.

The empty string is returned if there isn't a master controlling .cdx compound index tag or .idx index file (for example, SET ORDER TO is issued to display and access the table in natural record order).

nWorkArea

Specifies the work area number of the table for which SYS(22) returns the name of the master controlling .cdx compound index tag or .idx index file.

Reference