PCRETEST(1)                                                        PCRETEST(1)


NAME
       pcretest - a program for testing Perl-compatible regular expressions.


SYNOPSIS

       pcretest [options] [source] [destination]

       pcretest  was written as a test program for the PCRE regular expression
       library itself, but it can also be used for experimenting with  regular
       expressions.  This document describes the features of the test program;
       for details of the regular expressions themselves, see the  pcrepattern
       documentation. For details of the PCRE library function calls and their
       options, see the pcreapi documentation.


OPTIONS

       -b        Behave as if each regex has the /B (show bytecode)  modifier;
                 the internal form is output after compilation.

       -C        Output the version number of the PCRE library, and all avail-
                 able  information  about  the  optional  features  that   are
                 included, and then exit.

       -d        Behave  as  if  each  regex  has the /D (debug) modifier; the
                 internal form and information about the compiled  pattern  is
                 output after compilation; -d is equivalent to -b -i.

       -dfa      Behave  as if each data line contains the \D escape sequence;
                 this    causes    the    alternative    matching    function,
                 pcre_dfa_exec(),   to   be   used  instead  of  the  standard
                 pcre_exec() function (more detail is given below).

       -help     Output a brief summary these options and then exit.

       -i        Behave as if each regex  has  the  /I  modifier;  information
                 about the compiled pattern is given after compilation.

       -m        Output  the  size  of each compiled pattern after it has been
                 compiled. This is equivalent to adding  /M  to  each  regular
                 expression.   For  compatibility  with  earlier  versions  of
                 pcretest, -s is a synonym for -m.

       -o osize  Set the number of elements in the output vector that is  used
                 when  calling pcre_exec() or pcre_dfa_exec() to be osize. The
                 default value is 45, which is enough for 14 capturing  subex-
                 pressions   for  pcre_exec()  or  22  different  matches  for
                 pcre_dfa_exec(). The vector size can be changed for  individ-
                 ual  matching  calls  by  including  \O in the data line (see
                 below).

       -p        Behave as if each regex has the /P modifier; the POSIX  wrap-
                 per  API  is used to call PCRE. None of the other options has
                 any effect when -p is set.

       -q        Do not output the version number of pcretest at the start  of
                 execution.

       -S size   On  Unix-like  systems,  set the size of the runtime stack to
                 size megabytes.

       -t        Run each compile, study, and match many times with  a  timer,
                 and  output resulting time per compile or match (in millisec-
                 onds). Do not set -m with -t, because you will then  get  the
                 size  output  a  zillion  times,  and the timing will be dis-
                 torted. You can control the number  of  iterations  that  are
                 used  for timing by following -t with a number (as a separate
                 item on the command line). For example, "-t 1000" would iter-
                 ate 1000 times. The default is to iterate 500000 times.

       -tm       This is like -t except that it times only the matching phase,
                 not the compile or study phases.


DESCRIPTION

       If pcretest is given two filename arguments, it reads  from  the  first
       and writes to the second. If it is given only one filename argument, it
       reads from that file and writes to stdout.  Otherwise,  it  reads  from
       stdin  and  writes to stdout, and prompts for each line of input, using
       "re>" to prompt for regular expressions, and "data>" to prompt for data
       lines.

       When  pcretest  is  built,  a  configuration option can specify that it
       should be linked with the libreadline library. When this  is  done,  if
       the input is from a terminal, it is read using the readline() function.
       This provides line-editing and history facilities. The output from  the
       -help option states whether or not readline() will be used.

       The program handles any number of sets of input on a single input file.
       Each set starts with a regular expression, and continues with any  num-
       ber of data lines to be matched against the pattern.

       Each  data line is matched separately and independently. If you want to
       do multi-line matches, you have to use the \n escape sequence (or \r or
       \r\n, etc., depending on the newline setting) in a single line of input
       to encode the newline sequences. There is no limit  on  the  length  of
       data  lines;  the  input  buffer is automatically extended if it is too
       small.

       An empty line signals the end of the data lines, at which point  a  new
       regular  expression is read. The regular expressions are given enclosed
       in any non-alphanumeric delimiters other than backslash, for example:

         /(a|bc)x+yz/

       White space before the initial delimiter is ignored. A regular  expres-
       sion  may be continued over several input lines, in which case the new-
       line characters are included within it. It is possible to  include  the
       delimiter within the pattern by escaping it, for example

         /abc\/def/

       If  you  do  so, the escape and the delimiter form part of the pattern,
       but since delimiters are always non-alphanumeric, this does not  affect
       its  interpretation.   If the terminating delimiter is immediately fol-
       lowed by a backslash, for example,

         /abc/\

       then a backslash is added to the end of the pattern. This  is  done  to
       provide  a  way of testing the error condition that arises if a pattern
       finishes with a backslash, because

         /abc\/

       is interpreted as the first line of a pattern that starts with  "abc/",
       causing pcretest to read the next line as a continuation of the regular
       expression.


PATTERN MODIFIERS

       A pattern may be followed by any number of modifiers, which are  mostly
       single  characters.  Following  Perl usage, these are referred to below
       as, for example, "the /i modifier", even though the  delimiter  of  the
       pattern  need  not always be a slash, and no slash is used when writing
       modifiers. Whitespace may appear between the  final  pattern  delimiter
       and the first modifier, and between the modifiers themselves.

       The /i, /m, /s, and /x modifiers set the PCRE_CASELESS, PCRE_MULTILINE,
       PCRE_DOTALL, or PCRE_EXTENDED  options,  respectively,  when  pcre_com-
       pile()  is  called. These four modifier letters have the same effect as
       they do in Perl. For example:

         /caseless/i

       The following table shows additional modifiers for setting PCRE options
       that do not correspond to anything in Perl:

         /A              PCRE_ANCHORED
         /C              PCRE_AUTO_CALLOUT
         /E              PCRE_DOLLAR_ENDONLY
         /f              PCRE_FIRSTLINE
         /J              PCRE_DUPNAMES
         /N              PCRE_NO_AUTO_CAPTURE
         /U              PCRE_UNGREEDY
         /X              PCRE_EXTRA
         /<cr>           PCRE_NEWLINE_CR
         /<lf>           PCRE_NEWLINE_LF
         /<crlf>         PCRE_NEWLINE_CRLF
         /<anycrlf>      PCRE_NEWLINE_ANYCRLF
         /<any>          PCRE_NEWLINE_ANY
         /<bsr_anycrlf>  PCRE_BSR_ANYCRLF
         /<bsr_unicode>  PCRE_BSR_UNICODE

       Those  specifying  line  ending sequences are literal strings as shown,
       but the letters can be in either  case.  This  example  sets  multiline
       matching with CRLF as the line ending sequence:

         /^abc/m<crlf>

       Details  of the meanings of these PCRE options are given in the pcreapi
       documentation.

   Finding all matches in a string

       Searching for all possible matches within each subject  string  can  be
       requested  by  the  /g  or  /G modifier. After finding a match, PCRE is
       called again to search the remainder of the subject string. The differ-
       ence between /g and /G is that the former uses the startoffset argument
       to pcre_exec() to start searching at a  new  point  within  the  entire
       string  (which  is in effect what Perl does), whereas the latter passes
       over a shortened substring. This makes a  difference  to  the  matching
       process if the pattern begins with a lookbehind assertion (including \b
       or \B).

       If any call to pcre_exec() in a /g or  /G  sequence  matches  an  empty
       string,  the next call is done with the PCRE_NOTEMPTY and PCRE_ANCHORED
       flags set in order to search for another, non-empty, match at the  same
       point.   If  this  second  match fails, the start offset is advanced by
       one, and the normal match is retried. This imitates the way  Perl  han-
       dles such cases when using the /g modifier or the split() function.

   Other modifiers

       There are yet more modifiers for controlling the way pcretest operates.

       The /+ modifier requests that as well as outputting the substring  that
       matched  the  entire  pattern,  pcretest  should in addition output the
       remainder of the subject string. This is useful  for  tests  where  the
       subject contains multiple copies of the same substring.

       The  /B modifier is a debugging feature. It requests that pcretest out-
       put a representation of the compiled byte code after compilation.  Nor-
       mally  this  information contains length and offset values; however, if
       /Z is also present, this data is replaced by spaces. This is a  special
       feature for use in the automatic test scripts; it ensures that the same
       output is generated for different internal link sizes.

       The /L modifier must be followed directly by the name of a locale,  for
       example,

         /pattern/Lfr_FR

       For this reason, it must be the last modifier. The given locale is set,
       pcre_maketables() is called to build a set of character tables for  the
       locale,  and  this  is then passed to pcre_compile() when compiling the
       regular expression. Without an /L  modifier,  NULL  is  passed  as  the
       tables  pointer; that is, /L applies only to the expression on which it
       appears.

       The /I modifier requests that pcretest  output  information  about  the
       compiled  pattern (whether it is anchored, has a fixed first character,
       and so on). It does this by calling pcre_fullinfo() after  compiling  a
       pattern.  If  the pattern is studied, the results of that are also out-
       put.

       The /D modifier is a PCRE debugging feature, and is equivalent to  /BI,
       that is, both the /B and the /I modifiers.

       The /F modifier causes pcretest to flip the byte order of the fields in
       the compiled pattern that  contain  2-byte  and  4-byte  numbers.  This
       facility  is  for testing the feature in PCRE that allows it to execute
       patterns that were compiled on a host with a different endianness. This
       feature  is  not  available  when  the POSIX interface to PCRE is being
       used, that is, when the /P pattern modifier is specified. See also  the
       section about saving and reloading compiled patterns below.

       The  /S  modifier causes pcre_study() to be called after the expression
       has been compiled, and the results used when the expression is matched.

       The  /M  modifier causes the size of memory block used to hold the com-
       piled pattern to be output.

       The /P modifier causes pcretest to call PCRE via the POSIX wrapper  API
       rather  than  its  native  API.  When this is done, all other modifiers
       except /i, /m, and /+ are ignored. REG_ICASE is set if /i  is  present,
       and  REG_NEWLINE  is  set if /m is present. The wrapper functions force
       PCRE_DOLLAR_ENDONLY always, and PCRE_DOTALL unless REG_NEWLINE is  set.

       The  /8 modifier causes pcretest to call PCRE with the PCRE_UTF8 option
       set. This turns on support for UTF-8 character handling in  PCRE,  pro-
       vided  that  it  was  compiled with this support enabled. This modifier
       also causes any non-printing characters in output strings to be printed
       using the \x{hh...} notation if they are valid UTF-8 sequences.

       If  the  /?  modifier  is  used  with  /8,  it  causes pcretest to call
       pcre_compile() with the  PCRE_NO_UTF8_CHECK  option,  to  suppress  the
       checking of the string for UTF-8 validity.


DATA LINES

       Before  each  data  line is passed to pcre_exec(), leading and trailing
       whitespace is removed, and it is then scanned for \  escapes.  Some  of
       these  are  pretty esoteric features, intended for checking out some of
       the more complicated features of PCRE. If you are just  testing  "ordi-
       nary"  regular  expressions,  you probably don't need any of these. The
       following escapes are recognized:

         \a         alarm (BEL, \x07)
         \b         backspace (\x08)
         \e         escape (\x27)
         \f         formfeed (\x0c)
         \n         newline (\x0a)
         \qdd       set the PCRE_MATCH_LIMIT limit to dd
                      (any number of digits)
         \r         carriage return (\x0d)
         \t         tab (\x09)
         \v         vertical tab (\x0b)
         \nnn       octal character (up to 3 octal digits)
         \xhh       hexadecimal character (up to 2 hex digits)
         \x{hh...}  hexadecimal character, any number of digits
                      in UTF-8 mode
         \A         pass the PCRE_ANCHORED option to pcre_exec()
                      or pcre_dfa_exec()
         \B         pass the PCRE_NOTBOL option to pcre_exec()
                      or pcre_dfa_exec()
         \Cdd       call pcre_copy_substring() for substring dd
                      after a successful match (number less than 32)
         \Cname     call pcre_copy_named_substring() for substring
                      "name" after a successful match (name termin-
                      ated by next non alphanumeric character)
         \C+        show the current captured substrings at callout
                      time
         \C-        do not supply a callout function
         \C!n       return 1 instead of 0 when callout number n is
                      reached
         \C!n!m     return 1 instead of 0 when callout number n is
                      reached for the nth time
         \C*n       pass the number n (may be negative) as callout
                      data; this is used as the callout return value
         \D         use the pcre_dfa_exec() match function
         \F         only shortest match for pcre_dfa_exec()
         \Gdd       call pcre_get_substring() for substring dd
                      after a successful match (number less than 32)
         \Gname     call pcre_get_named_substring() for substring
                      "name" after a successful match (name termin-
                      ated by next non-alphanumeric character)
         \L         call pcre_get_substringlist() after a
                      successful match
         \M         discover the minimum MATCH_LIMIT and
                      MATCH_LIMIT_RECURSION settings
         \N         pass the PCRE_NOTEMPTY option to pcre_exec()
                      or pcre_dfa_exec()
         \Odd       set the size of the output vector passed to
                      pcre_exec() to dd (any number of digits)
         \P         pass the PCRE_PARTIAL option to pcre_exec()
                      or pcre_dfa_exec()
         \Qdd       set the PCRE_MATCH_LIMIT_RECURSION limit to dd
                      (any number of digits)
         \R         pass the PCRE_DFA_RESTART option to pcre_dfa_exec()
         \S         output details of memory get/free calls during matching
         \Z         pass the PCRE_NOTEOL option to pcre_exec()
                      or pcre_dfa_exec()
         \?         pass the PCRE_NO_UTF8_CHECK option to
                      pcre_exec() or pcre_dfa_exec()
         \>dd       start the match at offset dd (any number of digits);
                      this sets the startoffset argument for pcre_exec()
                      or pcre_dfa_exec()
         \<cr>      pass the PCRE_NEWLINE_CR option to pcre_exec()
                      or pcre_dfa_exec()
         \<lf>      pass the PCRE_NEWLINE_LF option to pcre_exec()
                      or pcre_dfa_exec()
         \<crlf>    pass the PCRE_NEWLINE_CRLF option to pcre_exec()
                      or pcre_dfa_exec()
         \<anycrlf> pass the PCRE_NEWLINE_ANYCRLF option to pcre_exec()
                      or pcre_dfa_exec()
         \<any>     pass the PCRE_NEWLINE_ANY option to pcre_exec()
                      or pcre_dfa_exec()

       The escapes that specify line ending  sequences  are  literal  strings,
       exactly as shown. No more than one newline setting should be present in
       any data line.

       A backslash followed by anything else just escapes the  anything  else.
       If  the very last character is a backslash, it is ignored. This gives a
       way of passing an empty line as data, since a real  empty  line  termi-
       nates the data input.

       If  \M  is present, pcretest calls pcre_exec() several times, with dif-
       ferent values in the match_limit and  match_limit_recursion  fields  of
       the  pcre_extra  data structure, until it finds the minimum numbers for
       each parameter that allow pcre_exec() to complete. The match_limit num-
       ber  is  a  measure of the amount of backtracking that takes place, and
       checking it out can be instructive. For most simple matches, the number
       is  quite  small,  but for patterns with very large numbers of matching
       possibilities, it can become large very quickly with increasing  length
       of subject string. The match_limit_recursion number is a measure of how
       much stack (or, if PCRE is compiled with  NO_RECURSE,  how  much  heap)
       memory is needed to complete the match attempt.

       When  \O  is  used, the value specified may be higher or lower than the
       size set by the -O command line option (or defaulted to 45); \O applies
       only to the call of pcre_exec() for the line in which it appears.

       If  the /P modifier was present on the pattern, causing the POSIX wrap-
       per API to be used, the only option-setting  sequences  that  have  any
       effect  are \B and \Z, causing REG_NOTBOL and REG_NOTEOL, respectively,
       to be passed to regexec().

       The use of \x{hh...} to represent UTF-8 characters is not dependent  on
       the  use  of  the  /8 modifier on the pattern. It is recognized always.
       There may be any number of hexadecimal digits inside  the  braces.  The
       result  is  from  one  to  six bytes, encoded according to the original
       UTF-8 rules of RFC 2279. This allows for  values  in  the  range  0  to
       0x7FFFFFFF.  Note  that not all of those are valid Unicode code points,
       or indeed valid UTF-8 characters according to the later  rules  in  RFC
       3629.


THE ALTERNATIVE MATCHING FUNCTION

       By   default,  pcretest  uses  the  standard  PCRE  matching  function,
       pcre_exec() to match each data line. From release 6.0, PCRE supports an
       alternative  matching  function,  pcre_dfa_test(),  which operates in a
       different way, and has some restrictions. The differences  between  the
       two functions are described in the pcrematching documentation.

       If  a data line contains the \D escape sequence, or if the command line
       contains the -dfa option, the alternative matching function is  called.
       This function finds all possible matches at a given point. If, however,
       the \F escape sequence is present in the data line, it stops after  the
       first match is found. This is always the shortest possible match.


DEFAULT OUTPUT FROM PCRETEST

       This  section  describes  the output when the normal matching function,
       pcre_exec(), is being used.

       When a match succeeds, pcretest outputs the list of captured substrings
       that  pcre_exec()  returns,  starting with number 0 for the string that
       matched the whole pattern. Otherwise, it outputs "No match" or "Partial
       match"  when  pcre_exec() returns PCRE_ERROR_NOMATCH or PCRE_ERROR_PAR-
       TIAL, respectively, and otherwise the PCRE negative error number.  Here
       is an example of an interactive pcretest run.

         $ pcretest
         PCRE version 7.0 30-Nov-2006

           re> /^abc(\d+)/
         data> abc123
          0: abc123
          1: 123
         data> xyz
         No match

       Note  that unset capturing substrings that are not followed by one that
       is set are not returned by pcre_exec(), and are not shown by  pcretest.
       In  the following example, there are two capturing substrings, but when
       the first data line is matched, the  second,  unset  substring  is  not
       shown.  An "internal" unset substring is shown as "<unset>", as for the
       second data line.

           re> /(a)|(b)/
         data> a
          0: a
          1: a
         data> b
          0: b
          1: <unset>
          2: b

       If the strings contain any non-printing characters, they are output  as
       \0x  escapes,  or  as \x{...} escapes if the /8 modifier was present on
       the pattern. See below for the definition of  non-printing  characters.
       If  the pattern has the /+ modifier, the output for substring 0 is fol-
       lowed by the the rest of the subject string, identified  by  "0+"  like
       this:

           re> /cat/+
         data> cataract
          0: cat
          0+ aract

       If  the  pattern  has  the /g or /G modifier, the results of successive
       matching attempts are output in sequence, like this:

           re> /\Bi(\w\w)/g
         data> Mississippi
          0: iss
          1: ss
          0: iss
          1: ss
          0: ipp
          1: pp

       "No match" is output only if the first match attempt fails.

       If any of the sequences \C, \G, or \L are present in a data  line  that
       is  successfully  matched,  the substrings extracted by the convenience
       functions are output with C, G, or L after the string number instead of
       a colon. This is in addition to the normal full list. The string length
       (that is, the return from the extraction function) is given  in  paren-
       theses after each string for \C and \G.

       Note that whereas patterns can be continued over several lines (a plain
       ">" prompt is used for continuations), data lines may not. However new-
       lines  can  be included in data by means of the \n escape (or \r, \r\n,
       etc., depending on the newline sequence setting).


OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION

       When the alternative matching function, pcre_dfa_exec(),  is  used  (by
       means  of  the \D escape sequence or the -dfa command line option), the
       output consists of a list of all the matches that start  at  the  first
       point in the subject where there is at least one match. For example:

           re> /(tang|tangerine|tan)/
         data> yellow tangerine\D
          0: tangerine
          1: tang
          2: tan

       (Using  the  normal  matching function on this data finds only "tang".)
       The longest matching string is always given first (and numbered  zero).

       If /g is present on the pattern, the search for further matches resumes
       at the end of the longest match. For example:

           re> /(tang|tangerine|tan)/g
         data> yellow tangerine and tangy sultana\D
          0: tangerine
          1: tang
          2: tan
          0: tang
          1: tan
          0: tan

       Since the matching function does not  support  substring  capture,  the
       escape  sequences  that  are concerned with captured substrings are not
       relevant.


RESTARTING AFTER A PARTIAL MATCH

       When the alternative matching function has given the PCRE_ERROR_PARTIAL
       return,  indicating that the subject partially matched the pattern, you
       can restart the match with additional subject data by means of  the  \R
       escape sequence. For example:

           re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
         data> 23ja\P\D
         Partial match: 23ja
         data> n05\R\D
          0: n05

       For  further  information  about  partial matching, see the pcrepartial
       documentation.


CALLOUTS

       If the pattern contains any callout requests, pcretest's callout  func-
       tion  is  called  during  matching. This works with both matching func-
       tions. By default, the called function displays the callout number, the
       start  and  current  positions in the text at the callout time, and the
       next pattern item to be tested. For example, the output

         --->pqrabcdef
           0    ^  ^     \d

       indicates that callout number 0 occurred for a match  attempt  starting
       at  the fourth character of the subject string, when the pointer was at
       the seventh character of the data, and when the next pattern  item  was
       \d.  Just  one  circumflex is output if the start and current positions
       are the same.

       Callouts numbered 255 are assumed to be automatic callouts, inserted as
       a  result  of the /C pattern modifier. In this case, instead of showing
       the callout number, the offset in the pattern, preceded by a  plus,  is
       output. For example:

           re> /\d?[A-E]\*/C
         data> E*
         --->E*
          +0 ^      \d?
          +3 ^      [A-E]
          +8 ^^     \*
         +10 ^ ^
          0: E*

       The  callout  function  in pcretest returns zero (carry on matching) by
       default, but you can use a \C item in a data line (as described  above)
       to change this.

       Inserting  callouts can be helpful when using pcretest to check compli-
       cated regular expressions. For further information about callouts,  see
       the pcrecallout documentation.


NON-PRINTING CHARACTERS

       When  pcretest is outputting text in the compiled version of a pattern,
       bytes other than 32-126 are always treated as  non-printing  characters
       are are therefore shown as hex escapes.

       When  pcretest  is  outputting text that is a matched part of a subject
       string, it behaves in the same way, unless a different locale has  been
       set  for  the  pattern  (using  the  /L  modifier).  In  this case, the
       isprint() function to distinguish printing and non-printing characters.


SAVING AND RELOADING COMPILED PATTERNS

       The  facilities  described  in  this section are not available when the
       POSIX inteface to PCRE is being used, that is, when the /P pattern mod-
       ifier is specified.

       When the POSIX interface is not in use, you can cause pcretest to write
       a compiled pattern to a file, by following the modifiers with >  and  a
       file name.  For example:

         /pattern/im >/some/file

       See  the pcreprecompile documentation for a discussion about saving and
       re-using compiled patterns.

       The data that is written is binary.  The  first  eight  bytes  are  the
       length  of  the  compiled  pattern  data  followed by the length of the
       optional study data, each written as four  bytes  in  big-endian  order
       (most  significant  byte  first). If there is no study data (either the
       pattern was not studied, or studying did not return any data), the sec-
       ond  length  is  zero. The lengths are followed by an exact copy of the
       compiled pattern. If there is additional study data, this follows imme-
       diately  after  the  compiled pattern. After writing the file, pcretest
       expects to read a new pattern.

       A saved pattern can be reloaded into pcretest by specifing < and a file
       name  instead  of  a pattern. The name of the file must not contain a <
       character, as otherwise pcretest will interpret the line as  a  pattern
       delimited by < characters.  For example:

          re> </some/file
         Compiled regex loaded from /some/file
         No study data

       When  the pattern has been loaded, pcretest proceeds to read data lines
       in the usual way.

       You can copy a file written by pcretest to a different host and  reload
       it  there,  even  if the new host has opposite endianness to the one on
       which the pattern was compiled. For example, you can compile on an  i86
       machine and run on a SPARC machine.

       File  names  for  saving and reloading can be absolute or relative, but
       note that the shell facility of expanding a file name that starts  with
       a tilde (~) is not available.

       The  ability to save and reload files in pcretest is intended for test-
       ing and experimentation. It is not intended for production use  because
       only  a  single pattern can be written to a file. Furthermore, there is
       no facility for supplying  custom  character  tables  for  use  with  a
       reloaded  pattern.  If  the  original  pattern was compiled with custom
       tables, an attempt to match a subject string using a  reloaded  pattern
       is  likely to cause pcretest to crash.  Finally, if you attempt to load
       a file that is not in the correct format, the result is undefined.


SEE ALSO

       pcre(3), pcreapi(3), pcrecallout(3),  pcrematching(3),  pcrepartial(d),
       pcrepattern(3), pcreprecompile(3).


AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.


REVISION

       Last updated: 18 December 2007
       Copyright (c) 1997-2007 University of Cambridge.
