Last December, PWS posted an article in defense of skipping heading levels (e.g., from H2 to H5) in the accessibility context. You could skip straight to my detailed response, or read this post first; it’s more-or-less by way of a summary.
It’s sometimes more accessible to skip heading levels, PWS writes, and five examples are offered to make the point that PDF/UA is wrong in prohibiting this practice. In the examples given, the PWS article asserts that heading levels should be assigned roles as follows:
- Example 1: Skipping from H1 to H3 indicates that content is “off the main narrative”
- Example 2: H5 is assigned to “Environmental Issues”
- Example 3: H4 is assigned to “Case Studies”
- Example 4: H4 is assigned to “Drivers”
- Example 5: H3 is assigned to “Topics”; the absence of H3 is supposed to imply a single topic within the respective H2.
Instead of making the intended point, the examples instead reveal:
- The author is willing to consider headings as an indicator of narrative and/or importance and/or editorial classification in addition to the conventional best-practice role of section organization, and
- The author is enamored of one specific AT reading method: scanning at a specific heading level
It’s certainly true that if one consistently assigns heading levels to specific classes of information and then successfully communicates that strategy, AT users with the ability to skip through headings at the same level will be able to focus on that information.
This approach may work well with content designed to suit the strategy and users briefed to receive it, but no further. Accessibility standards require generic rules and meanings and cannot assume such design nor such briefings. Since the PWS strategy is conditional on both, it’s properly excluded from PDF/UA.
One most bear in mind two key facts:
- Assigning heading levels to roles other than section headings complicates (or eliminates) the use of the same heading level for conventional best-practice document structuring purposes, as my simple extension of Ted’s example 3 makes clear.
- If such assignments exist, communicating them is vital to understanding the structure of the document (especially because they can cause conflicts with standard practice). However, these assignments aren’t in any way programmatically discernable; the role assigned to heading levels in such cases is only available via the user’s observational skills, or an explicit briefing from the author.
Unlike WCAG 2.0, which does not regard headings as critical for web content navigation, PDF/UA reflects the fact that headings provide the only possibility of high-quality AT navigation of document structure in PDF.
It’s for this simple reason that PDF/UA requires that if authors use heading levels at all those levels must makes sense as hierarchical section headings, whatever other role they bear in addition.
Much as some might wish otherwise, today’s PDF simply doesn’t include any structured content-classification model for tags (but it’s a very interesting idea for future development of ISO 32000).
To be sure, ensuring that heading levels express the hierarchical organization of content places a burden on document authors. Sometimes a re-design of poorly structured content is required. On the other hand; so what? There are plenty of other accessibility considerations that require reconsideration or redevelopment of content. Good heading structures are vital for AT navigation of PDF content, so why fight it?
Authors can certainly use headings to indicate case studies or racing-car drivers, or anything else, but those are styling, not structure considerations.
Some want headings to deliver more information than just the document’s structure; they want a customizable, content-specific road-map to the document. I think that’s great, and I like the idea. First though, everyone needs to be able to understand and use the same systems in the same ways.
If unreliable, low-performance navigation for AT users in PDF files is the problem (and it’s certainly one of the problems), then standardized use of heading levels is the cure.