missing-alt-text

All codes

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

What happened

Under PDF/UA-1, a page has a Figure or Formula element without alternate text: neither /Alt (Tag::with_alt) nor /ActualText (Tag::with_actual_text).

Why

A screen reader can’t describe a picture or a formula by itself. The PDF/UA-1 standard for accessible PDF (ISO 14289-1 §7.3) requires every Figure and every Formula to carry a text alternative. These are conditions 13-004 and 17-002 of the Matterhorn Protocol, the PDF Association’s checklist of PDF/UA failures. Lamina PDF checks only that a description exists; whether it describes the figure well is for a person to judge.

How to fix

Describe the figure with Surface::figure(&image, rect, alt) or Tag::new(TagKind::Figure).with_alt(…). If the picture is decoration that carries no meaning, draw it inside Surface::artifact instead.

Example

surface.tag(TagKind::Figure, |s| { s.image(&chart, rect); Ok(()) })?;
builder.finish()?; // missing-alt-text: use Tag::new(TagKind::Figure).with_alt("Sales by month")

Data fields

• page: the page’s index (0-based).