Matterhorn 01-007 · PDF/UA-1 UA1:7.1-11
Suspects true: the producer's own warning about its tagging
The MarkInfo dictionary carries /Suspects true, which is the producing application's own declaration that its tagging may be unreliable. PDF/UA-1 requires the value to be false.
The condition, as the protocol states it. “Suspects entry has a value of true.”
Matterhorn Protocol 1.1, checkpoint 01, index 01-007, section UA1:7.1-11. Software can decide this one on its own.
What a screen reader actually does
No direct effect, but the flag tells conforming processors that the structure cannot be trusted; some will fall back to raw content order.
What is in the file
The document Catalog carries a /MarkInfo dictionary. It has at most three keys, and two of them matter here:
/MarkInfo << /Marked true /Suspects true >>/Marked true says the document has a structure tree. /Suspects true says the producer is not confident that structure describes the content correctly. ISO 32000-1 defines it as indicating the presence of “tagged content that may not adhere to the tagging rules” — in practice, tags the producing application inferred rather than knew.
Absence is the default. A file with no /Suspects key is treated as /Suspects false, and passes. Only the explicit true fails.
Why the standard refuses it
PDF/UA-1 clause 7.1 requires that the document does not carry /Suspects true. The reasoning is direct: the whole standard rests on the structure tree being an accurate description of the content. A file that ships with its producer’s own warning attached is asserting two contradictory things at once — here is the structure and do not rely on the structure.
A conforming processor is permitted to act on the warning. Nothing in the specification obliges it to keep using a structure tree the file itself has flagged, which means the reading order you can see in the Tags panel is not guaranteed to be the reading order anyone gets.
What it usually means in practice
Acrobat sets the flag from its own auto-tagging. When you run Autotag Document on an untagged file, Acrobat infers structure from visual properties — font size becomes heading level, ruled lines become table borders, column geometry becomes reading order — and sets /Suspects true when its confidence in those inferences is low.
So the flag is a useful signal rather than an obstacle. A file carrying it almost always also carries:
- Headings inferred from size. Text that was bold and 16pt became an H2; a pull quote that happened to be 16pt became one too.
- A reading order that follows the page, not the document. Multi-column layouts are the usual casualty, and right-to-left ones are the worst case: Acrobat walks left to right, which is backwards for a Hebrew two-column page.
- Tables assembled from lines. If the table used whitespace alignment rather than ruled borders, there is no table at all.
- Figures with no alt text, since nothing can infer that.
Clearing /Suspects is a one-line change. The work the flag is pointing at is not.
How to check it free
Acrobat Pro’s Accessibility Check reports it under Document as Tagged PDF — Failed in some versions and does not report it at all in others, which makes it unreliable for this specific condition.
veraPDF reports it against clause 7.1 directly and is the tool to trust here.
Command line. /MarkInfo is in the Catalog, usually uncompressed:
grep -a Suspects document.pdfIf the cross-reference stream is compressed you will see nothing; qpdf --qdf --object-streams=disable document.pdf out.pdf first, then grep out.pdf.
How to fix it free, in Acrobat Pro
Acrobat has no interface control for this entry. The free routes are:
- Preflight fixup.
Print Production → Preflight, search the fixups for Suspects, and run the one that removes it. Present in Acrobat Pro DC and later. - Re-tag properly and let Acrobat clear it. If you rebuild the structure by hand in the Tags panel rather than by auto-tagging, Acrobat does not re-set the flag on save.
Whichever route, do the structural review first. The flag exists to tell you the tagging was guessed; removing it removes the only record that anyone was warned.
Where Taggart differs
clear-suspects is a safe fix — it touches one boolean, no content, no structure — but Taggart will not run it in isolation from the rest of the batch, and the remediation report says so explicitly.
The reason is the one above. A file whose only reported failure is /Suspects true is unusual and mildly suspicious in itself; a file that carries it alongside inferred headings and a page-order reading sequence is the normal case, and clearing the flag there produces a document that passes one more machine test and reads exactly as badly as before.
So Taggart reports 01-007 with the other findings on the same file next to it, and where the document also shows heading inference or reading-order problems, the report records that the flag was cleared and what else was found at the same time. That pairing is what makes the audit trail worth anything: it shows the warning was read before it was switched off.
How Taggart handles it
Taggart detects this condition automatically. It is reported as a blocker, with the page, the structure path and the object id of every occurrence.
The fix is Clear the Suspects flag. It is mechanical, so “Fix All Safe” applies it in bulk with a diff and a single undo.
Whatever Taggart changes, the page still looks identical. Fixes edit the PDF object model, not the content streams, and every remediation is re-rendered and compared against the original at structural similarity ≥ 0.999 before you get the file back. A tool that quietly reflows your document is worse than no tool.
Frequently asked questions
Can I just set it to false?
Mechanically, yes — it is one boolean. Honestly, only after you have looked. The flag is usually set because an auto-tagger could not decide something: a heading it inferred from font size, a table it built from ruled lines, a reading order it guessed from column positions. Clearing the flag without checking those is telling a validator the tagging is trustworthy on no evidence.
Which tools set it?
Acrobat's Autotag Document sets it whenever its own confidence heuristics fire. Several PDF libraries set it unconditionally when they write a structure tree, which is why some files carry it despite having hand-authored tags.
Does any screen reader read this flag?
No mainstream reader changes behaviour on it. The specification allows a conforming processor to distrust the structure tree when Suspects is true and fall back to content order, and some validators and preflight tools do exactly that, but JAWS, NVDA and VoiceOver do not.
Where is it in the file?
The Catalog's /MarkInfo dictionary: << /Marked true /Suspects true >>. Absent means false, which is why a file with no /Suspects key passes this condition.
Where this sits in the standards
| Standard | Reference |
|---|---|
| Matterhorn Protocol 1.1 | Checkpoint 01 (Real content tagged), index 01-007 |
| PDF/UA-1 (ISO 14289-1) | Clause 7.1-11 |
| WCAG 2.1 | 1.3.1 Info and Relationships — Level A |
| EN 301 549 / Section 508 / ADA Title II | All three point at WCAG 2.1 Level AA for non-web documents, so a Level A or AA criterion here is in scope for each of them. |
Related conditions
- 01-005 Content is neither marked as Artifact nor tagged as real content Every text-showing, image-painting and path-painting operator on a page must sit either inside a marked-content sequence that maps to the structure tree, or inside an artifact sequence. Content that is in neither is orphaned.
- 09-001 Tags are not in logical reading order The order of elements in the structure tree does not match the order a human would read the page. This is the single most common substantive defect in tagged PDFs and the one Acrobat's own tooling handles worst.
- 14-001 Headings are not tagged Text that is visually a heading — larger, bolder, isolated — is tagged as a paragraph. The document has no navigable outline.
- 02-001 Non-standard tag mapping does not terminate with a standard type A custom tag name is present in the role map but the chain of mappings never arrives at a structure type defined in ISO 32000-1, 14.8.4. Mapping may be indirect — a custom type may map to another custom type — but it must eventually terminate.
Other conditions in checkpoint 01
Checkpoint 01 covers real content tagged. These are its other failure conditions; the ones without a link are in the rule set but do not have a written page yet.
- 01-001 Artifact tagged as real content Decoration — a rule line, a page-border image, a watermark, a background flourish — has been given a real content tag, so assistive technology announces it as if it were part of the document.
- 01-002 Real content marked as artifact Content that carries meaning has been marked as an artifact, which removes it from the structure tree entirely. This is the most damaging single mistake in PDF remediation because the content becomes invisible rather than merely mis-labelled.
- 01-003 Content marked as Artifact is present inside tagged content A BMC/BDC artifact sequence has been opened while a marked-content sequence for real content is still open. Artifacts and real content may not be nested inside one another.
- 01-004 Tagged content is present inside content marked as Artifact A marked-content sequence for real content has been opened inside an open artifact sequence. The artifact swallows the real content.
- 01-005 Content is neither marked as Artifact nor tagged as real content Every text-showing, image-painting and path-painting operator on a page must sit either inside a marked-content sequence that maps to the structure tree, or inside an artifact sequence. Content that is in neither is orphaned.
- 01-006 Structure type is not semantically appropriate The tag does not match the nature of the content: a heading tagged as a paragraph, a data table tagged as a layout container, a caption tagged as body text. This is the judgment call that no validator can make for you.
Check your own file. Taggart’s validator is free and unlimited — every machine-checkable Matterhorn condition, no page cap, no watermark, no account needed.
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