Document full text search

Author: rouilj

doc/user_guide.txt

@@ -375,6 +375,22 @@ You may manually write URLS that contain these arguments, like so
         @filters=status,keyword&
         @columns=title,status,fixer
 
+Full text search using the xapian, whoosh and native indexers treats
+the search query as a series of space separated words. Any word less
+than 2 characters or more than 25 characters is discarded. Also a
+stoplist is used to remove common words like "with", "and"
+etc. Additional stoplist words can be added in the tracker's
+config.ini file. Once filtering of the word list is done, each indexed
+item (e.g. title, file or message content ...) is searched and if all
+the terms are found in the item the item is returned. Then the items
+are mapped to an issue and the list of matching issues is generated.
+
+Other searching backends such as native-fts can be used in which case
+the filtering above is not used. The search query can support
+structure such as quoted phrases, matching one term or another rather
+than both (or search), prefixes etc. In this case you should look at
+the documentation for the native-fts backend to find the supported
+format and features.
 
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