NOTE: Have been receiving lots of questions concerning the accessibility of math and scientific formulas in PDF documents. This post is the first in a series of how to make STEM content accessible in different document content.
Sometimes just complying with basic standards is not enough if you want your PDF document content to be accessible to all assistive technologies.
Case in point: consider STEM (Science, Technology, Engineering, and Mathematics) formulas.
According to PDF/UA accessibility guidelines, “All mathematical expressions shall be enclosed within a Formula tag and shall have an ALT attribute.”
How to Describe an Equation
Have a look at this math equation:
You have to remember that the screen reader user is listening to the equation, so its ALT text description would be set to:
ALT=”m equals begin fraction m sub 0 over begin square root 1 minus begin fraction v sup 2 over c sup 2 end fraction end square root end fraction” [SOURCE]
Advice from Adobe
“Because speech software may handle Formula tags differently from normal text, it may be necessary to add a description using alternate text.”
…according to Ted Page of Accessible Digital Documents, if you do so, the content may not be read by some earlier versions of the NVDA screen reader, with or without an ALT attribute.
Solutions That You Should Test
- Nest a <P> tag in the Formula tag that has a text alternative in an Actual Text attribute. This content can be accessed by NVDA.
- The Formula tag is an inline level element. If it is used as a block level element, the attribute “Placement: Block” is required. Otherwise some assistive technologies are not able to present it correctly. Follow these steps:
1. In the Acrobat Pro Tags pane, right click the Formula tag.
2. Select Properties.
3. On the Tag tab of the Object Properties dialog, click the Edit Attribute Objects button.
4. In the Attributes dialog, if there is not a “/Attribute Object # <<Dictionary>>” item, click the New Item button.
5. Select “/Attribute Object # <<Dictionary>>” and click the New Item button.
6. In the Add Key and Value dialog, enter Placement in the Key field, and Block in the Value field. Leave Name as the Value Type.
7. Click OK.
Whether you have limited experience with the PDF remediation process, are expanding your knowledge on how to remediate PDFs, or simply need a resource that can help remind you how to fix a frustrating error, the info provided in this e-book can help.