Before we start, let us try to revisit these questions: what is a filter and what is it for? In simple terms, a filter is used to narrow the search space or, in another words, search within a search. Filter and Query may seem to provide the same functionality, but there is a significant difference between the two. Scores are calculated in querying to rank results, based on their relevancy to the search terms, while a filter has no effect on scores. It's not uncommon that users may prefer to navigate through a hierarchy of filters in order to land on the relevant results. You may often find yourselves in a situation where it is necessary to refine a result set so that users can continue to search or navigate within a subset. With the ability to apply filters, we can easily provide such search refinements. Another situation is data security where some parts of the data in the index are protected. You may need to include an additional filter behind the scene that...