@awb right - the original plan was to create a curses gui more like GNU info than "nroff | more" for display of the SGML man pages allowing for following links & other advanced features, but it was never completed. All that ever shipped was a pipeline to convert SGML to nroff to view the pages the traditional way when you ran the man command.
The SGML support was removed from the man command in Solaris 11.4 after we finished the SGML to XML conversion for all the man page sources.