hfy-split-index

hfy-split-index is a variable defined in `htmlfontify.el'.
Its value is

nil

Documentation:
Whether or not to split the index `hfy-index-file' alphabetically.
If non-nil, the index is split on the first letter of each tag.
Useful when the index would otherwise be large and take
a long time to render or be difficult to navigate.

You can customize this variable.