PDF/UA-1 · CLAUSE 7.4.2
Heading structure is inconsistent
The document mixes strongly structured headings (H1, H2, H3) with weakly structured H tags, skips heading levels, or nests more than one H under a single node.
Why it matters
Heading navigation is the primary way screen reader users skim a document. Skipped or inconsistent levels break the outline they navigate by.
How to fix it
- Pick one model: numbered headings (H1..H6) throughout, or H tags throughout, never both in the same file.
- Start at H1 and do not skip levels when descending (H1 > H2 > H3).
- Fix heading levels in the source document's paragraph styles so every export is correct.
What the standard says
For documents that are not strongly structured, as described in ISO 32000-1:2008, 14.8.4.3.5, heading tags shall be used as follows: (*) If any heading tags are used, H1 shall be the first. (*) A document may use more than one instance of any specific tag level. For example, a tag level may be repeated if document content requires it. (*) If document semantics require a descending sequence of headers, such a sequence shall proceed in strict numerical order and shall not skip an intervening heading level. (*) A document may increment its heading sequence without restarting at H1 if document semantics require it
Check your own PDF
Validate a file against PDF/UA-1 and see whether this rule fails in your document.
curl -sS -X POST "https://api.ua1.dev/api/validate?format=compact&profile=ua1" \ -F "file=@document.pdf"