@c This file is part of the GNU Dico manual.
@c Copyright (C) 2012--2021 Sergey Poznyakoff
@c This file is distributed under GFDL 1.1 or any later version
@c published by the Free Software Foundation.
  This appendix summarizes search strategies available for use in Dico
@value{VERSION}.

@table @asis
@item exact
@cindex exact, a strategy
Match words exactly.  This is a built-in strategy.

@item prefix
@cindex prefix, a strategy
Match word prefixes.  This is a built-in strategy.

@item nprefix
@cindex nprefix, a strategy
This strategy is similar to @samp{prefix}, except that it allows the
user to limit the number of returned matches.  If the search term has
the structure @samp{@var{skip}#@var{count}#@var{string}}, where @var{skip}
and @var{count} are integer numbers, then the @samp{nprefix} strategy
will return at most @var{count} headwords that begin with
@var{string}, omitting first @var{skip} unique matches.

This strategy is implemented in the @file{nprefix} loadable module.
@xref{nprefix}.

@item suffix
@cindex suffix, a strategy
Match word suffixes.  This is a built-in strategy.

@item soundex
@cindex soundex, a strategy
Match words using SOUNDEX algorithm@footnote{See
@uref{http://en.wikipedia.org/wiki/Soundex}}.  This strategy matches  
headwords that sound approximately the same as the search term.
Note, that it is suitable only for English words.

This is a built-in strategy.

@item lev
@cindex lev, a strategy
Match headwords within given Levenshtein distance (1 by default).
This strategy accounts for the most usual spelling errors.

@cindex distance, Levenshtein
@cindex Levenshtein distance
The Levenshtein distance between two strings is the minimum number of
@dfn{edits} needed to transform one string into the other.  The
edits are: insertion, deletion, or substitution of a single character.
Thus, Levenshtein distance 1 means that only one such operation
suffices to convert one string to another.  This is the default for
that strategy.

This built-in strategy is used as a default one (@pxref{default
strategy}), unless the @code{default-strategy} configuration statement
mandates otherwise.

The dictionary server may optionally allow users to alter the
Levenshtein distance using the extension command @code{XLEV}.  This
command is enabled by setting the @samp{xlev} capability.
@xref{Capabilities, xlev}, for a detailed description.

@item nlev
@cindex nlev, a strategy
Match normalized headwords within given Levenshtein distance.  This
strategy is similar to @samp{lev}, except that it treats any runlength
of whitespace characters appearing in a headword as a single space
(ASCII 32) character.

@item dlev
@cindex dlev, a strategy
Match headwords within given Damerau-Levenshtein distance (1 by
default).

The Damerau-Levenshtein distance extends the Levenshtein distance by
an additional edit operation: transposition of two adjacent
characters.

This strategy is similar to @samp{lev}, but covers a much wider range of
spelling and typographical errors.

The distance threshold optionally be configured using the @code{XLEV}
command (@pxref{Capabilities, xlev}).

@item ndlev
@cindex ndlev, a strategy
This is the same as @samp{dlev}, except that it treats any runlength
of whitespace characters appearing in a headword as a single space
(ASCII 32) character.

@item re
@cindex re, a strategy
Match using POSIX 1003.2 regular expressions.  This strategy treats
the search term as a regular expression (@pxref{Extended
regexps, Extended regular expressions, Extended regular expressions,
sed, GNU sed}).

@item regexp
@cindex regexp, a strategy
Match using basic regular expressions.

@item pcre
@cindex pcre, a strategy
Match using Perl-compatible regular expressions.  This strategy is
implemented in the loadable module @file{pcre}.  @xref{pcre}.

@item all
@cindex all, a strategy
Match everything.  This experimental strategy ignores its argument and
matches all headwords.  It is implemented in the @file{stratall}
module, which you must load if you wish to make that strategy
available.  @xref{stratall}.

@item substr
@cindex substr, a strategy
Match a substring anywhere in the headword.  This strategy is
implemented as a loadable module.  @xref{substr}.

@item word
@cindex word, a strategy
Match a word anywhere in the headword.  This is one of the strategies
provided by the @file{word} loadable module.  @xref{word}.

@item first
@cindex first, a strategy
Match the first word within headwords.  This strategy is
implemented in @file{word} loadable module.  @xref{word}.

@item last
@cindex last, a strategy
Match the last word within headwords.  This strategy is
implemented in @file{word} loadable module.  @xref{word}.

@end table

  
