Links export to PDF creates "Null Alt Text" attribute in tagged PDF
When an ID 15 file with hyperlinks is exported to Tagged PDF, unless you assign alternative text to the Links in ID, the Link tags will have a "null text" attribute which prevents the content of the Link tag from being read by a screen reader. This is a problem for several reasons. Not everyone chooses to add alternative text to hyperlinks. It's a UA, but not a WCAG 2 requirement. An automated accessibility checker like Acrobat's or even PAC is not going to flag this. Most people do not do a "Jaws check" of the PDF they are remediating and will never know that the links are not "reading."
Also, if you have a Figure which is hyperlinked the proper structure for that in a 508 compliant PDF is to place the Figure tag inside the Link tag and assign alternative text to the Figure tag not the link tag. Now with the null text Link tags, THIS will produce a "nested link" error from the Acrobat Checker. The nested alternative text for the Figure will not be read. Unfortunately, many people attempting to make 508 PDFs are unaware of what "null alt text" is and will have a devil of a time trying to resolve the error.
So, instead of making PDF remediation easier with this new feature in ID you have made things worse!
Ideally if no alternative text is entered in Indesign there should be no Alt text attribute of any kind in the Link Tag in the PDF.
I've attached several files so you can see what this looks like in the Tags panel, but to truly understand it you should try to "read" the attached PDF using a screen reader like Jaws or NVDA.
The fix for this issue is now available in the latest update of InDesign – that is, InDesign 15.0.2.
Please update your InDesign application to get this fix.
Adobe InDesign team
R Benedetto commented
See attached files which were somehow not included in the above post. Also good information about "null" text (in this case, null actual text, but same effect) can be found here https://taggedpdf.com/508-pdf-help-center/actual-text-with-null-string/
Ted Page commented
Hyperlinks created in InDesign 15.0.1 are not read at all by screen readers when exported to PDF (although the tags look fine, ie, parent Link tag and child Link-OBJR and link text tags). You have to recreate the links from scratch in Acrobat as things currently stand.
All previous versions of InDesign, going back to version 5.5 create accessible links out of the box.
This functionality is broken in InDesign 15.
This is a really serious problem that needs to be fixed asap.