No skipped heading levels

ZMD002

Ensure headings (`<h1>`–`<h6>`) follow a logical, sequential order to maintain a clear document outline.

<h2>Main section</h2>
<h3>Subpoint</h3>
<p>Details…</p>

<h2>Main section</h2>
<h4>Subpoint</h4>
<p>Details…</p>

When: A heading level is more than one step deeper than the previous heading

Warning: Heading level skipped: <hX> after <hY>

Solution: Follow sequential heading order

Accessibility: Skipping levels disrupts screen-reader users’ mental model of document structure and impairs navigation.

SEO: Misordered headings can confuse search engine crawlers about content hierarchy.

Goal: Maintain a nested document structure via proper heading nesting.
What to do: Do not jump more than one level (e.g. `<h2>` → `<h4>`).
Why: Screen readers and sighted users rely on heading order to understand hierarchy and navigate content.

Prevent confusion in document structure by enforcing sequential heading levels without skips.

Consistent outline improves comprehension for users with cognitive disabilities.
Screen-reader users can predict content flow and navigate headings linearly.
Search engines better understand content hierarchy, aiding SEO.

Each heading tag defines a section in the outline; skipping levels breaks the implicit tree structure.