unnumbered-heading-misused

All codes

• Type: error
• Kind: usage (the caller misused the API)

What happened

Under PDF/UA-1, the document misuses the unnumbered heading H, a heading whose level comes from the section it sits in. Numbered headings are H1, H2 and so on. Either two H elements share one parent, or the document uses H and numbered headings together.

Why

A screen reader works out an H heading’s level from the sections around it. A section therefore has one H at most, and a document that mixes the two kinds gives no consistent outline. The PDF/UA-1 standard for accessible PDF (ISO 14289-1 §7.4.4) requires one H per section and only one kind of heading per document. These are conditions 14-006 and 14-007 of the Matterhorn Protocol, the PDF Association’s checklist of PDF/UA failures.

How to fix

Use numbered headings (TagKind::H1 to TagKind::H6) throughout; most documents need nothing else. If you use H (Tag::custom("H", …)), give each section (Sect) its own and leave the numbered ones out.

Example

s.text("Results", &font, Pt::new(18.0), at)?.tag(TagKind::H1);
s.text("Method", &font, Pt::new(14.0), at2)?.tag(Tag::custom("H", TagKind::H2));
builder.finish()?; // unnumbered-heading-misused: use TagKind::H2 for the second heading

Data fields

• page: the page’s index (0-based).