#help_index "Topic/SubTopic;OtherTopic"
The help index preprocessor compiler directive sets the topics for symbols subsequently defined.  You specify subtopics with a 
'/' tree hierarchy and separate multiple topics with a ';'.  The index ctrls HI:index links.

public causes a symbol to appear in help_index reports.

#help_file "filename[.DD]"
The help file preprocessor directive makes a file into the heading of a HI:index report for the current help index.