I'm working on a standard, simple way to do faceted searching based on metadata in the HTML header which is encoded in a standardized manner, and how to optimize that using eXist index configuration. I've made a lot of progress, using DC Terms vocabulary in meta tags in the header (supplemented with some custom stuff in our own scheme space) and range indexes. I've also been tangling with the issue of switchable content based on choice elements; ideally, we would be able to switch in the interface between a diplomatic transcription and a normalized one, by hiding and showing various elements, which is fine; but I'd also like to allow searching in the same way, which requires creating parallel indexes in which components are ignored. This can't be done with current eXist capabilities because you cannot tell the indexer to ignore elements based on predicates (here attribute values), and these elements will all be spans distinguished by classes. Still working on this right now.