By @Mikhail Fokanov

1. Is there any requirements regarding relevancy, namely - See: 
     a. If text contains consequent words from query it should be higher, than text, in which there is “War” and “Peace” but they are presented not consequently
     b. Should relevancy be based on availability of items
     c. Any other requirements?

2. Should it be a sort field selection, what is the list of sort fields
     a. Should any relevancy algorithms be applied, the sort is not “By relevancy

3. Should filters on left-hand side be narrowed and counters for each particular filter are shown
Actually this is pretty common functionality and it is named Faceted search (for a description see for example: - See: UXPROD-902

E.g. if user search for “War and Peace”, for example in “Nature of Content” he will see: audiobook (5), textbook (125), etc.
     a. Should the facets be hierarchical (e.g. user can filter for all “computer” formats or just for “computer – computer disc”)?

4. Is search over instance and items and holding fields at the same time a must have feature, considering, that it increases the cost of implementation and the data storage maintenance cost?
E.g. search for some title and location name in the same query: “War and peace some_location_name
     a. Or maybe instances items and holdings searches can be completely separate searches?

5.  Is there a requirement to do stemming and stop words filtering?
E.g. if user searches for “streams“ system should include results with “stream”
     a. If this requirement should be implemented, what is the list of support languages and is there a field in MARC, in which the language code is supposed to be set

6. What fields should be searchable using full text search algorithms (e.g. by particular words with stemming etc.)?

7. What fields are supposed to be search only by exact match?
E.g. if user mistype the id, Folio shouldn’t show any results and shouldn’t suggest him anything

8. What are the requirements regarding smart search?
     a. Should we fully support CQL
     b. Or just support bool commands like: NOT (title : "War")
     c. Or filtering by facets (see point 3) might replace this functionality
Additional features, that could be implemented in future, but should be considered from the beginning in order not to have an architecture incompatible with their implementation

9. Is there requirements about Autocomplete:
     a. Should it be based only on title and author fields?
     b. Actually the most efficient autocomplete in ES works only from the beginning of the phrase (only removing stop words)

10. Did you mean, e.g. if user type “health car”, there should be a clickable hint in UI: “did you mean: health care”

11. If one of the word is missed in the instance should we still find some results and stroke out the missing word (e.g. like Google often do in such case)