When used with any of the arguments ‘cim’, this option is the opposite of ‘-x’. See -x.
The option ‘-XI’ tells FWEAVE to write its index
cross-references to a file formatted for input by the makeindex
utility. This feature facilitates creation of a master index that spans
several individual web files. For more discussion, see
Using makeindex.
The construction ‘-XI’ stands alone; one may not mix the ‘I’ with the list ‘cim’. Also, this option is overridden by ‘-xi’, which suppresses output of all index information.