DITA Specializations in Native PDF Publishing (Topics Disappear in PDF)

DITA Specializations in Native PDF Publishing (Topics Disappear in PDF)

We have one DITA specialization that appears to be properly configured in AEM Guides. I can insert it and use it in the XML Editor in topics and concepts.

In previous AEM Guides versions, this specialization appeared in PDF outputs, but that may have been using FMPS before Native PDF Publishing was released. I don't recall if I ever tested it in the earlier versions of Native PDF Publishing. We abandoned this specialization because there was no easy way to format it for the AEM Sites output. However, we'd like to return to using this specialization (which is based on the PARML element) since DITA is designed for easy customization and future releases will make it easier to format the AEM Sites outputs.

The specialization appears in the default DITA-OT PDF output. It is unformatted (expected behavior) because there is no easy to way format the DITA-OT files, but it does appear.

Currently (AEM Guides v4.6), the DITA specialization does the following:
1. In Native PDF Publishing output, any topic with the specialization does not appear in the PDF output. No title/heading, no content, no entry in the table of contents.
2. In AEM Sites output, any topic with the specialization is listed in the table of contents, but the output for that topic is empty/blank.
3. In the default DITA-OT output, the specialization appears, but is unformatted (expected behavior since these are the default DITA-OT files that aren't customized.)

What went wrong? Why does it appear that this specialization is correctly set up in the AEM Guides configuration, but doesn't output in Native PDF Publishing?