Doc updates for indexers.

change word size max from 25 to 50

phrase search syntax updated

clear up wording for automatic selection of xapian/whoosh

link user_guide to admin_guide for finding syntax for native_fts
searches.

Author: rouilj

doc/admin_guide.txt

@@ -305,7 +305,7 @@ https://www.sqlite.org/fts5.html#full_text_query_syntax. This
 supports:
 
   * plain word search (joined with and similar to other search methods)
-  * phrase search with terms enclosed in ``"`` quotes
+  * phrase search with terms enclosed in quotes (``"``)
   * proximity search with varying distances using ``NEAR()``
   * boolean operations by grouping with parentheses and using ``AND``
     and ``OR``
@@ -346,7 +346,7 @@ languages are supported.
 Websearch provides a more natural style of search and supports:
 
 * plain word search (stemmed in most cases)
-* phrase search with terms enclosed in quotes
+* phrase search with terms enclosed in quotes (``"``)
 * exclusion by prefixing a term/phrase with ``-``
 * alternative/or searching with ``or`` between terms
 * ignores non-word characters including punctuation

doc/upgrading.txt

@@ -119,15 +119,16 @@ that have both of those words (an AND search) in a text-field (like
 title) or in a message (or file) attached to the issue.
 
 One thing to note is that native-fts searches do not ignore words
-longer than 25 characters or less than 2 characters. Also SQLite does
-not filter out common works (i.e. there is no stopword list). So words
+longer than 50 characters or less than 2 characters. Also SQLite does
+not filter out common words (i.e. there is no stopword list). So words
 like "and", "or", "then", "with" ...  are included in the FTS5 search.
 
 You must explicitly enable this search mechanism by changing the
-``indexer`` setting in ``config.ini`` to ``native-fts``. Native-fts is
-never chosen by default like xapian or whoosh. This prevents the
-existing native indexing from being discarded if ``indexer`` is not
-set.
+``indexer`` setting in ``config.ini`` to ``native-fts``. Native-fts
+must be explicitly chosen. This is different from Xapian or Whoosh
+indexers, which are chosen if they are installed in the Python
+environment. This prevents the existing native indexing from being
+discarded if ``indexer`` is not set.
 
 Next re-index your data with ``roundup-admin -i tracker_home
 reindex``. This can take a while depending on the size of the tracker.

doc/user_guide.txt

@@ -377,7 +377,7 @@ You may manually write URLS that contain these arguments, like so
 
 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
+than 2 characters or more than 50 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
@@ -389,8 +389,10 @@ 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.
+the `documentation for configuring the native-fts`_ backend to find
+the supported format and features.
+
+.. _`documentation for configuring the native-fts`: admin_guide.html#configuring-native-fts-full-text-search
 
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