I was looking at your documented CHMspec pages a while ago.
Specifically, the page located at:
http://chmspec.nongnu.org/latest/Sitemap.html#HHK_Name

I was looking at the pages in response to a message containing a plea for help asking about the second name parameter for the CHM .HHK file.
As there seems to be nothing that really documents this and your pages seem to be the sole repository, I wondered if my response might be helpful in some way.

Here is what I replied with on HATT moments ago:

I cannot tell you what Microsoft may call the second name parameter, but I can tell you what it controls.

When you compile a CHM and are creating Index entries you establish relationships between each term or phrase the user sees in the list of terms and whatever topics are associated with each term or phrase.

So the first Name parameter stores what appears in the list of terms.

As the user finds interesting terms or phrases and clicks them, one of two things occurs, depending on the configuration of the Index.

If the term or phrase is associated to a single topic, the topic appears in the topic pane of the CHM viewer.
If the term or phrase is associated with multiple topics, a pop up list of potential topics is presented. In this case, what is configured in the second Name parameter is presented to the user. When clicked, its associated topic appears in the topic pane of the CHM viewer.

Note that if you have perhaps four CHM topics associated with a specific term or phrase, you will then see five Name parameters listed. Each additional parameter is also followed by a "Local" parameter that lists the path and file name to the associated topic.

Cheers... Rick :)