added open fast trace requirements for backend search

docs/requirements/backend-search.md

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+---
+parent: Requirements
+---
+# Backend Search
+Search functionalities the backend needs to support.
+
+## General Search
+Standard search functions.
+
+### Word Matching
+`req~backend-search.general-search.word-matching~1`
+
+Searching for a word retrieves all entries containing it.
+Searching for multiple words only returns entries containing all of them.
+
+### Sequence Matching
+`req~backend-search.general-search.sequence-matching~1`
+
+Searching for a sequence of words only lists entries containing the words of the sequence in the given order.
+Searching for multiple sequences lists entries containing all sequences.
+
+### Combinations
+`req~backend-search.general-search.combinations~1`
+
+Searching for words and sequences at the same time is allowed and results in a list of entries containing all words and sequences.
+<!-- What should happen when searching for a word and a sequence containing the word? -->
+
+### Case Sensitivity
+`req~backend-search.general-search.case-sensitivity~1`
+
+Allow searching for words and sequences with and without respecting case sensitivity.
+
+### Normalisation of Terms
+`req~backend-search.general-search.normalisation~1`
+
+Terms with varying spelling get detected and are searched in all commonly known variations. E.g. Searching for `Düsseldorf` will also find entries containing `Duesseldorf`, `Dusseldorf` and `D\"{u}sseldorf` and vice versa.
+
+## Field Search
+Search functions using the fields that bibliographic data provides. E.g. Author, date, title, url and more.
+
+### Field Contains
+`req~backend-search.field-search.field-contains~1`
+
+Fields are searchable for contained words and sequences. Listing entries with the specified field which contains the searched word or sequence.
+<!-- Inherent anyfield search is not a requirement, but a neat implementation feature. -->
+
+### Field Matches
+`req~backend-search.field-search.field-matches~1`
+
+Fields are searchable for exact matches. I.e. words or sequences.
+E.g. `year == 1932` searches for entries with the year field being exactly 1932, assuming "==" is the symbol for "matches".
+
+### Field Search Combinations
+`req~backend-search.field-search.combinations~1`
+
+Searches can be logically combined using boolean operations.  
+Concatenate two search phrases with `and` and only results that fulfill both conditions are shown.  
+Use `or` between two search phrases to list entries that satisfy either one or both.  
+Prepend a search phrase with `not` to invert the resulting entry list, showing all entries that would have been hidden.  
+Finally, using `(` and `)` to isolate a part of the logical operations to ensure its resolution before the standard left to right order.
+
+Note that the symbols used here are just an example.
+
+### Pseudo Fields
+`req~backend-search.field-search.pseudo-fields~1`
+
+The following four pseudo fields are supported: anyfield, anykeyword, key and entrytype.  
+
+- Searching for a word or sequence in any field is possible and returns entries that have a field containing the searched word or sequence.  
+- Search among the keywords is supported, listing entries when the given phrase is part of its keywords.  
+- Searching for citation keys will show entries containing the phrase in their citation key or show the single entry whose key matches the phrase (in case of an exact match search).  
+- Entries of a certain type can be listed. E.g. `entrytype = thesis` lists all entries whose type contains `thesis`, like `bachelorsthesis` or `mastersthesis`.
+
+## Searching with Regular Expressions
+Search function requirements regarding the support of regular expressions. In the case of JabRef, specifically refer to [java regular expressions](https://docs.oracle.com/en/java/javase/16/docs/api/java.base/java/util/regex/Pattern.html).
+
+### Regular Expressions Search
+`req~backend-search.regex-search~1`
+
+When searching, regular expressions as defined in Java can be used.
+This means the backend is searchable with special characters (e.g. tab: `\t`, carriage-return: `\r`), with character classes (e.g. `[a-z]`), with boundary matchers (e.g. `\b`, `\B`), greedy, reluctant and possessive quantifiers (e.g. `?`, `*`, `+`) and logical operators (e.g. braces: `(` `)`, or: `|`).  
+Searching with special characters by escaping them is also supported.
+
+<!-- markdownlint-disable-file MD022 -->