How are levels determined in HTML5 outputs?

I would have just conditionalized them both to be Print only & skipped having them in the HTML5 output altogether. But YMMV ;>)

Problem solved! Here is the solution, hope this would help another HTML5 newbie with a similar issue.

Problem

• In the FM book, the hierarchy for front and rear cover files are identical, at the top level.
• However, in the HTML5 output, the front cover is at the top level while the rear cover is much lower in hierarchy, hidden inside other folders. 
• During trial, I copied the front cover and renamed it as the rear cover, hence they are the same document. However, the mismatch of HTML5 levels for front and rear cover continues.

Reasons for mismatch of HTML5 TOC levels

Note: In my book, the names of FM files for front and back covers are ‘Front_cover_HTML.fm’ and ‘Rear_cover_HTML.fm.’ However, these files appear in the HTML5 TOC as ‘Front cover’ and ‘Rear cover.’ This is because the front and rear cover files contain the text ‘Front cover’ and ‘Rear cover’ that has a ‘Title_hidden’ paragraph style (white text on white page).

• The front cover was the 1st file in the book, hence was at the top of the TOC hierarchy. This is why that name appears at the highest level.
• The rear cover’s title paragraph style was at a lower hierarchy as compared to the Heading 1 or Title paragraph style of the Fault-finding.fm file.

Learning that led to the solution

• The font size, font weight or first indent hierarchy determines the hierarchy of HTML5 TOC. (reference: https://community.adobe.com/t5/framemaker-discussions/missing-toc-nesting-in-html5-publish-output/m-p/7575012).
• The name displayed in the HTML5 TOC is the first paragraph style in the page.
• The indent in the TOC determines the nesting inside the HTML5 TOC.

Solution

• Move the ‘Front cover’ and ‘Rear cover’ text in ‘Title_hidden’ paragraph style as the first entry on the front and rear cover FM files. This pushes the page to the top of the hierarchy in the HTML5 TOC.