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Lamina PDF

invalid-structure-nesting

All codes

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

What happened

Under PDF/UA-1, a table or list element sits in a parent its type doesn’t allow. A table (Table) holds rows (TR), each holding header cells (TH) and data cells (TD); a list (L) holds list items (LI), each holding a label (Lbl, its bullet or number) and a body (LBody). Examples of a wrong parent: a TD or TH outside a TR, a TR outside a Table, an LI outside an L, or a paragraph directly inside a Table, TR, L or LI.

Why

ISO 32000-1 Tables 336 and 337 define how tables and lists are built, and assistive technology relies on that shape to announce rows, columns and list items. The PDF/UA-1 standard for accessible PDF (ISO 14289-1 §7.2) requires tables and lists to have that shape. These are conditions 09-004 and 09-005 of the Matterhorn Protocol, the PDF Association’s checklist of PDF/UA failures.

How to fix

Nest tables as Table > TR > TH or TD (optionally with THead, TBody and TFoot around the rows, and a Caption), and lists as L > LI > Lbl and LBody. Put paragraphs and other content inside the cells and list bodies.

Example

s.tag(TagKind::Table, |s| {
    s.text("Total", &font, Pt::new(11.0), at)?.tag(TagKind::TD); // a TD straight in the Table
    Ok(())
})?;
builder.finish()?; // invalid-structure-nesting: wrap the cell in a TR

Data fields

  • page: the page’s index (0-based).
  • kind: the element’s standard type, such as TD.
  • parent: its parent’s standard type (Document at the top level).