The .index heading command substitutes the heading text as the header for index pages. The heading text is output on the top of each index page.
.index heading text
.ixh
.index heading Topics covered .index ’Topic 1’ ’Topic 2’ .index ’Topic 3’ .index ’Topic 4’ .xindex .print index
Produces this output:
Topics covered Topic 1,1 Topic 2,1 Topic 3,1 Topic 4,1