Consider a scenario where you are implementing faceted navigation and you want to let the user pick several values of a field to filter on instead of just one. Typically, when an individual facet value is chosen, this becomes a filter. The filter makes subsequent faceting on that field almost pointless because the filter filters out the possibility of seeing other facet choices—assuming a single-valued field. In this scenario, we'd like to exclude this filter for this facet field.

The preceding screenshot is from http://search-lucene.com, in which you can search across the mailing lists, API documentation, and other places that have information about Lucene, Solr, and other related projects. This screenshot shows that it lets users choose more than one type of information to filter results on at the same time, by letting users pick as many check boxes as they like.

We'll demonstrate the problem that multiselect faceting solves with a MusicBrainz example...