If paragraphs, tables, headings and lists are jumbled together their content is inaccessible; in PDF this can happen all too often. A document’s logical reading order can be a challenge in PDF for four key reasons:
- Many PDF files are made by software that’s just incapable of making tagged PDF in the first place.
- Some software can make tagged PDF but does a poor job.
- Even with software capable of creating high-quality tagged PDF, many users don’t bother to properly order their content in the authoring application (such as PowerPoint).
- PDF is extremely flexible; certain situations are just difficult to tag correctly in the authoring software due to visual requirements for the content.
To illustrate the challenge posed by PDF’s flexibility, consider the following image, which shows a two-page spread from a magazine. In such cases, a single tag (for the heading) must include content from more than one page.
Ensuring text and other content is tagged in logical reading order is perhaps the single most important aspect of making content in PDF accessible because it’s the tags that deliver headings, paragraphs, lists, images and other content on PDF pages in the correct sequence to assistive technology users.
Not only must all content be tagged, not only must all content be tagged with appropriate semantics, but these tags must appear in an order that’s appropriate, reflecting the flow of content in the document.
CommonLook PDF provides two methods for checking reading order. The Readability checkpoint, accessible via the Section 508 and Verify and Remediate modes, provides a red highlight that moves across page content in the order of tags.
The default speed is set fairly slow to help you get acquainted with the feature; about 1 second per document element. Within a few seconds you’ll get the idea, and quickly decide you’ll want an increased speed, in which case you simply reduce the time per element, as shown in the image above.
Set the speed to the desired level to see the highlight move through the active page in tag order.
Another way to understand reading-order in CommonLook PDF is to simply change settings in the Logical View to hide boxes. The plain-text is shown in the left-side logical view while the corresponding section of the actual page is highlighted on the right.
CommonLook PDF orients content order to logical reading order
Unlike other software, CommonLook PDF aligns the output PDF’s content order to match the logical reading order. This allows software that doesn’t understand tagged PDF to nonetheless deliver readable results, even if the document’s semantics (headings, lists and so on) aren’t present.
Learn more about using CommonLook PDF to check and correct logical reading order.
What Failure Looks Like
- If the Readability checkpoint’s highlight doesn’t follow the logical reading order
- If the order of text in the logical view doesn’t match what you see in the physical view
- If your assistive technology doesn’t read the document in order
Readability is a basic requirement in all standards and guidelines for accessible content, including WCAG 1.0, WCAG 2.0, PDF/UA, the State of Oklahoma standards, and others.
PDF/UA requires that reading order be valid in section 7.2.
WCAG 2.0 addresses the question of “meaningful sequence” in Success Criteria 1.3.2.
The 2001 Section 508 requirements (§1194.22 (d)) require documents to be “readable without an associated style-sheet” which is universally understood to apply to the sequence of content in PDF.