Idea

When trying to understand how is_title works - the search leads me to this page: https://docs.vectara.com/docs/learn/metadata-search-filtering/ootb-metadata-filters

This only mentions that part.is_title is a default field, but I think it's worthwhile to better explain how titles are handled in our system more broadly. From my understanding:

1. During indexing: how are document-level and section-level titles indexed?
2. How are titles used at query time if no filter is specified? if using a filter condition of "is_title.part=true" and if using a filter condition of "is_title.part<>true"
3. Are titles included in matching during query-time?
4. General guidance on how/when to use is_title as a filter.