Heading Order must be appropriate
How to Fix the Problem
Ensure headings are in a logical order. Check that all headings are marked with H1 through H6 tags and that these are ordered hierarchically. For example, the heading level following an H1 tag should be an H2 tag, not an H3 tag.
Why it Matters
When heading elements are applied correctly, the page becomes much easier to navigate for screen reader users and sighted users alike. In the same way that sighted users can glance at a page and get a sense of its contents, users of screen readers can do the same by navigating through headings. Properly tagged headings can save users, especially those who use screen readers, a lot of time and frustration.
Rule Description
Headings must be in a valid logical order, meaning H1 through H6 element tags must appear in a sequentially-descending order.
The Algorithm (in simple terms)
Ensure the order of headings is sequential.