Tagged PDF and PDF/UA

In Tagged PDF, ‘TH’ structure elements may have a ‘Scope’ attribute, and both ‘TH’ and ‘TD’ structure elements may have a ‘Headers’ attribute. PDF/UA requires some features in a conforming PDF/UA file that are only optional in ordinary PDF. This includes ‘Headers’ attributes and, where ‘Headers’ attributes are not clear enough, also ‘Scope’ attributes.

The good news about accessible table markup is that any XML vocabulary that supports (X)HTML-compatible table markup supports ‘scope’ and ‘headers’ attributes. For example, ‘scope’ and ‘headers’ are in both JATS and DocBook as side-effects of their supporting HTML tables.

The not-so-good news about accessible table markup is that it requires human effort to properly markup the relationships between table cells, especially for convoluted tables. In practice, the attributes are poorly understood and are often omitted. For example, the JATS 1.2 tag library currently omits ‘scope’ and ‘headers’ from its ‘Accessibility’ page, notes that ‘scope’ (though not ‘headers’) has not been widely supported, and inaccurately states that ‘headers’ points to rows and columns when it actually points to individual header cells.