PDF heading order

Silktide checks that the headings in a PDF go down one level at a time. Heading levels describe how a document nests, so a level one followed directly by a level three leaves a gap that makes the document's shape ambiguous.

Headings are numbered one to six, and the number is the only thing that says what belongs inside what. A level two heading is a chapter of the level one above it; a level three is a section of that chapter. Skipping a level breaks the relationship rather than just the numbering.

Why this matters

Heading levels are the table of contents builds for itself. users navigate long documents by jumping between headings and by moving up and down levels, which is how someone finds one clause in a hundred-page policy without reading the ninety-nine that precede it. That only works when the levels are truthful.

When a level is skipped, a reader hearing "heading level three" after a level one cannot tell what happened. Perhaps a section was missed. Perhaps this is a subsection of something they never heard. The usual reason for the skip is visual: someone needed a smaller-looking heading and picked the style that looked right rather than the level that was right. The appearance was the goal and the structure was collateral damage.

Consistent levels also make a document more usable for everyone, because they are what generate a reliable table of contents, bookmarks, and navigation panes.

How to fix it

Fix the levels at the source. In Word, use Heading 1, Heading 2, and Heading 3 in order; in InDesign, map paragraph styles to the correct export tags. Then re-export.
Separate the level from the look. If a level two heading is too large for the design, restyle the level two rather than promoting the text to a level three. Levels carry meaning, size does not.
Do not skip a level to fill space, and do not use a heading for emphasis. Bold text is for emphasis; a heading announces a new section.
Check the start of the document too. Headings should begin at level one, and each document normally has exactly one.
Or run Silktide remediation, which reviews the heading hierarchy against the document as a reader sees it. See How PDF remediation works.

How Silktide tests this

Find the PDF documents linked from your website, and analyze each unique file once however many pages link to it.
Read the heading tags in the order the structure tree gives them.
Report the document when a heading is more than one level below the heading before it.
Report each document once, however many skips it contains.

Going back up several levels at once is normal and is not reported: a level four followed by a level two simply ends a subsection and starts a new one.

Troubleshooting

The document has no headings at all

Then this check has nothing to examine, and the problem is a different one. A long document with no headings cannot be navigated by structure at all, which the accessibility review reports separately.

My headings look right on the page

Appearance and level are independent, and this check reads the level. A document can look impeccably organized while its tags claim a structure nobody intended, usually because heading styles were applied by eye. The screen reader preview shows the outline as assistive technology receives it.

The skip is in an appendix or a covering letter

Structure still applies. If a section genuinely sits at the top of the document's hierarchy, tag it at level one, and if it belongs inside the section above it, tag it one level below. There is no need to reflect its importance through the numbering.