@DavidCarlisle I've got sorting working for
tex-faq.github.io/category - I think tags are more-or-less the same, just starting from different data. My idea at the moment is to alter the main page to say something like 'Here are the questions in categories: each question appears once. You can also see (some) questions by tag [here]: not all questions are tagged, some have multiple tags'. Does that sound OK?