This is not the final website. It is a demo of the real tool working, made for Y Combinator.
AxisRemedy

14-005 Content representing a 7th level (or higher) heading does not use an <H7> (or higher) tag.

A heading deeper than level 6 is not tagged H7 or higher.

Checkpoint
14: Headings
ISO 14289-1 (PDF/UA-1) clause
7.4.3-1
Test type in the protocol
Needs a human judgement
Applies to
A single object

How AxisRemedy handles it

Left for you, with screening. A person has to judge this one. AxisRemedy looks for signs of a problem and lists the places to look at, with the page and a box around the spot. It never reports a pass or a fail for this condition.