The PDF Formula tag and accessible mathematical expressions

22nd April 2018 | by Ted Page

Part 2 of: why standards compliance does not (necessarily) equate to accessible PDF

Just a very short post this month due to very high workload. Hopefully normal service will be resumed in the next few weeks.

In part one of this series we took our first look at the subject of when content producers need to go beyond standards compliance in order to ensure that documents are accessible to all assistive technologies. In that case it was in the context of ensuring that a PDF’s non-tags’ reading order is correct. The PDF Formula tag is another potential problem area that document authors need to be aware of. 


If you include mathematical expressions in a PDF, in order to ensure that the file is PDF/UA compliant, you must tag them with Formula tags. The relevant rule in PDF/UA 1.0 is 7.7 Mathematical expressions, which states that: 

All mathematical expressions shall be enclosed within a Formula tag as detailed in ISO 32000-1:2008, and shall have an Alt attribute.

However, if you do so, the content will not be read by NVDA, with or without an Alt attribute (although it works fine with JAWS).

The solution

This problem could, of course, be fixed by NVDA fairly easily. But that is exactly the point—eventually standards compliance and accessibility may be the same thing, but we are not there yet. And until we are, document authors need to:

  • test everything with multiple assistive technologies
  • know when to break the rules in order to ensure that content is accessible.

For now your best bet is probably a <P> tag with the text alternative in an Actual Text attribute. This will work fine in NVDA, JAWS and SuperNova. It won’t work in the latter if you use an Alt attribute.