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From: Claire Forbes
Date: Jun 17, 2025 2:21PM
Subject: <H> tags within PDF
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Good afternoon,
Working within a PDF, CommonLook has been flagging documents for "document uses both unnumbered and numbered heading tags."
The document title on the cover page is tagged as an <H> tag, it is the only <H> tag within the document, as the rest of the document follows the proper heading level hierarchy tagging as appropriate.
Why does CommonLook consider this a failure? What WCAG standard does this align with that makes it a failure - can anyone further explain?
Thank you so much!
Claire Forbes
Section 508 Specialist
From: Paul Rayius
Date: Jun 17, 2025 2:58PM
Subject: Re: <H> tags within PDF
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Hi Claire,
This is a good question; thanks for asking!
CommonLook PDF throws a failure when a PDF has both <H> and <Hn> (numbered heading) tags because that is a violation of PDF/UA-1. That said, to address your "other" question, "where does this fail in WCAG": It's important to note that while the WCAG standard does apply very well to PDF, because HTML (web) and PDF are different technologies there is not always a 1:1 mapping between requirements. That said, when it comes to PDF, where there is not a direct alignment between the two specifications, the requirements for PDF have to "win."
I hope that helps explain CommonLook's approach.
Best,
Paul
Paul Rayius, ADS
VP, Customer Support and Training
P: +1 800 563 0668 x5209
E: = EMAIL ADDRESS REMOVED =
Visit us online:
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Allyant was formed by combining the best web and document accessibility brands (T‑Base, CommonLook, and Accessible360).
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From: Claire Forbes
Date: Jun 18, 2025 7:43AM
Subject: Re: <H> tags within PDF
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Thank you for your reply.
I guess what I’m trying to understand it why is having one <H> tag considered non-compliant when the rest of the heading tags are <H1> or <H2>, <H3>
From: Paul Rayius < = EMAIL ADDRESS REMOVED = >
Sent: Tuesday, June 17, 2025 4:58 PM
To: WebAIM Discussion List < = EMAIL ADDRESS REMOVED = >
Cc: Claire Forbes < = EMAIL ADDRESS REMOVED = >
Subject: RE: <H> tags within PDF
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IRONSCALES couldn't recognize this email as this is the first time you received an email from this sender prayius @ allyant.com
Hi Claire,
This is a good question; thanks for asking!
CommonLook PDF throws a failure when a PDF has both and (numbered heading) tags because that is a violation of PDF/UA-1. That said, to address your "other" question, "where does this fail in WCAG": It's important to note that while the WCAG standard does apply very well to PDF, because HTML (web) and PDF are different technologies there is not always a 1:1 mapping between requirements. That said, when it comes to PDF, where there is not a direct alignment between the two specifications, the requirements for PDF have to "win."
I hope that helps explain CommonLook's approach.
Best,
Paul
Paul Rayius, ADS
VP, Customer Support and Training
P: +1 800 563 0668 x5209
E: = EMAIL ADDRESS REMOVED = <mailto: = EMAIL ADDRESS REMOVED = >
Visit us online:
allyant.com
Allyant was formed by combining the best web and document accessibility brands (T‑Base, CommonLook, and Accessible360).
Read our story.
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From: Paul Rayius
Date: Jun 18, 2025 7:52AM
Subject: Re: <H> tags within PDF
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That is the rule, as explicitly stated in the PDF/UA-1 standard (ISO 14289). You are not “allowed” to have both numbered and non-numbered headings in an accessible PDF. For PDF/UA-1 compliance, you can use <H> or <Hn> but not both.
Paul Rayius
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VP, Customer Support and Training
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From: Claire Forbes < = EMAIL ADDRESS REMOVED = >
Sent: Wednesday, June 18, 2025 9:43 AM
To: Paul Rayius < = EMAIL ADDRESS REMOVED = >; WebAIM Discussion List < = EMAIL ADDRESS REMOVED = >
Subject: RE: <H> tags within PDF
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Thank you for your reply.
I guess what I’m trying to understand it why is having one <H> tag considered non-compliant when the rest of the heading tags are <H1> or <H2>, <H3>
From: Paul Rayius < = EMAIL ADDRESS REMOVED = <mailto: = EMAIL ADDRESS REMOVED = >>
Sent: Tuesday, June 17, 2025 4:58 PM
To: WebAIM Discussion List < = EMAIL ADDRESS REMOVED = <mailto: = EMAIL ADDRESS REMOVED = >>
Cc: Claire Forbes < = EMAIL ADDRESS REMOVED = <mailto: = EMAIL ADDRESS REMOVED = >>
Subject: RE: <H> tags within PDF
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IRONSCALES couldn't recognize this email as this is the first time you received an email from this sender prayius @ allyant.com
Hi Claire,
This is a good question; thanks for asking!
CommonLook PDF throws a failure when a PDF has both and (numbered heading) tags because that is a violation of PDF/UA-1. That said, to address your "other" question, "where does this fail in WCAG": It's important to note that while the WCAG standard does apply very well to PDF, because HTML (web) and PDF are different technologies there is not always a 1:1 mapping between requirements. That said, when it comes to PDF, where there is not a direct alignment between the two specifications, the requirements for PDF have to "win."
I hope that helps explain CommonLook's approach.
Best,
Paul
Paul Rayius, ADS
VP, Customer Support and Training
P: +1 800 563 0668 x5209
E: = EMAIL ADDRESS REMOVED = <mailto: = EMAIL ADDRESS REMOVED = >
Visit us online:
allyant.com
Allyant was formed by combining the best web and document accessibility brands (T‑Base, CommonLook, and Accessible360).
Read our story.
E-mail Notification: The information contained in this email and any attachments is confidential and may be subject to copyright or other intellectual property protection. If you are not the intended recipient, you are not authorized to use or disclose this information, and we request that you notify us by reply mail or telephone and delete the original message from your mail system.
From: Duff Johnson
Date: Jun 18, 2025 7:53AM
Subject: Re: <H> tags within PDF
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> Thank you for your reply.
> I guess what I’m trying to understand it why is having one <H> tag considered non-compliant when the rest of the heading tags are <H1> or <H2>, <H3>
Well, what heading level is that “H” heading tag? What role does it serve in the document’s structure?
The reason “H” cannot be used alongside H1, H2, etc is that it’s impossible to know what the “H” means with respect to the other headings in the document.
Duff.
From: Philip Kiff
Date: Jun 18, 2025 8:34AM
Subject: Re: <H> tags within PDF
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Hi Claire,
Here are some additional references that support what Paul and Duff say.
When a PDF mixes H headings with H1-6 headings, it means that it is
mixing two different kinds of PDF structuring methods: "Strongly
structured" (using only H's and relying on grouping and nesting to
determine relative values), and "Weakly structured" (using a relatively
flat structure, but relying on the numbering level of the H1-Hn to
determine hierarchy). These structuring methods are defined in PDF
32000-1 in section 14.8.4.3.5 Usage Guidelines for Block-Level Structure.
The PDF/UA-1 specification adds a bit of explicit clarification that
"All documents shall be either strongly or weakly structured, but not
both." at section 7.4.4 in ISO 14289-1.
The PDF/UA-2 specification says that you must use only the "Weakly
structured" method, and so all H's in PDF/UA-2 have to be H1-Hn, as
explained at section 8.2.5.12 Heading (Hn) and (H) in ISO 14289-2.
For WCAG compliance, this would fail under Success Criterion 1.3.1 Info
and Relationships, I think.
Though having said all that, I doubt that there is any real world
accessibility effect on any real person using assistive technology if
the only Heading that uses the unnumbered type of heading is the very
first heading in the document.
Phil.
Philip Kiff
D4K Communications
On 2025-06-18 9:43 a.m., Claire Forbes via WebAIM-Forum wrote:
> Thank you for your reply.
> I guess what I’m trying to understand it why is having one <H> tag considered non-compliant when the rest of the heading tags are <H1> or <H2>, <H3>
>
> From: Paul Rayius <snip>
> Sent: Tuesday, June 17, 2025 4:58 PM
> To: WebAIM Discussion List< = EMAIL ADDRESS REMOVED = >
> Cc: Claire Forbes <snip>
> Subject: RE: <H> tags within PDF
>
> Hi Claire,
> This is a good question; thanks for asking!
> CommonLook PDF throws a failure when a PDF has both and (numbered heading) tags because that is a violation of PDF/UA-1. That said, to address your "other" question, "where does this fail in WCAG": It's important to note that while the WCAG standard does apply very well to PDF, because HTML (web) and PDF are different technologies there is not always a 1:1 mapping between requirements. That said, when it comes to PDF, where there is not a direct alignment between the two specifications, the requirements for PDF have to "win."
> I hope that helps explain CommonLook's approach.
> Best,
> Paul
>
> Paul Rayius, ADS
> VP, Customer Support and Training
>
From: David Farough
Date: Jun 18, 2025 9:28AM
Subject: Re: <H> tags within PDF
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Thanks Philip;
That makes sense to me.
I wonder if the document author was trying to improve navigability for screen readers by using the heading tag. The title style does not translate to anything useful for access technology.
Until now I didn't realize that you could not mix the two methods and be compliant.