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INFO-DIR-SECTION Utilities
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* ZSH: (zsh).                     The Z Shell Manual.
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File: zsh.info,  Node: Completion Functions,  Next: Completion Directories,  Prev: Bindable Commands,  Up: Completion System

Utility Functions
=================

Descriptions follow for utility functions that may be useful when
writing completion functions.  If functions are installed in
subdirectories, most of these reside in the Base subdirectory.  Like
the example functions for commands in the distribution, the utility
functions generating matches all follow the convention of returning
zero if they generated completions and non-zero if no matching
completions could be added.

Two more features are offered by the _main_complete function.  The
arrays compprefuncs and comppostfuncs may contain names of functions
that are to be called immediately before or after completion has been
tried.  A function will only be called once unless it explicitly
reinserts itself into the array.

_all_labels [ -x ] [ -12VJ ] TAG NAME DESCR [ COMMAND ARGS ... ]
     This is a convenient interface to the _next_label function below,
     implementing the loop shown in the _next_label example.  The
     COMMAND and its arguments are called to generate the matches.  The
     options stored in the parameter NAME will automatically be inserted
     into the ARGS passed to the COMMAND.  Normally, they are put
     directly after the COMMAND, but if one of the ARGS is a single
     hyphen, they are inserted directly before that.  If the hyphen is
     the last argument, it will be removed from the argument list
     before the COMMAND is called.  This allows _all_labels to be used
     in almost all cases where the matches can be generated by a single
     call to the compadd builtin command or by a call to one of the
     utility functions.

     For example:

          local expl
          ...
          if _requested foo; then
            ...
            _all_labels foo expl '...' compadd ... - $matches
          fi

     Will complete the strings from the matches parameter, using
     compadd with additional options which will take precedence over
     those generated by _all_labels.

_alternative [ -C NAME ] SPEC ...
     This function is useful in simple cases where multiple tags are
     available.  Essentially it implements a loop like the one
     described for the _tags function below.

     The tags to use and the action to perform if a tag is requested are
     described using the SPECs which are of the form:
     `TAG:DESCR:ACTION'.  The TAGs are offered using _tags and if the
     tag is requested, the ACTION is executed with the given
     description DESCR.  The ACTIONs are those accepted by the
     _arguments function (described below), excluding the `->STATE' and
     `=...' forms.

     For example, the ACTION may be a simple function call:

          _alternative \
              'users:user:_users' \
              'hosts:host:_hosts'

     offers usernames and hostnames as possible matches, generated by
     the _users and _hosts functions respectively.

     Like _arguments, this functions uses _all_labels to execute the
     actions, which will loop over all sets of tags.  Special handling
     is only required if there is an additional valid tag, for example
     inside a function called from _alternative.

     Like _tags this function supports the -C option to give a
     different name for the argument context field.

_arguments [ -swWACRS ] [ -O NAME ] [ -M MATCHSPEC ] [ : ] SPEC ...
     This function can be used to give a complete specification for
     completion for a command whose arguments follow standard UNIX
     option and argument conventions.  The following forms specify
     individual sets of options and arguments; to avoid ambiguity,
     these may be separated from the options to _arguments itself by a
     single colon.

    N:MESSAGE:ACTION
    N::MESSAGE:ACTION
          This describes the N'th normal argument.  The MESSAGE will be
          printed above the matches generated and the ACTION indicates
          what can be completed in this position (see below).  If there
          are two colons before the MESSAGE the argument is optional.
          If the MESSAGE contains only white space, nothing will be
          printed above the matches unless the action adds an
          explanation string itself.

    :MESSAGE:ACTION
    ::MESSAGE:ACTION
          Similar, but describes the _next_ argument, whatever number
          that happens to be.  If all arguments are specified in this
          form in the correct order the numbers are unnecessary.

    *:MESSAGE:ACTION
    *::MESSAGE:ACTION
    *:::MESSAGE:ACTION
          This describes how arguments (usually non-option arguments,
          those not beginning with - or +) are to be completed when
          neither of the first two forms was provided.  Any number of
          arguments can be completed in this fashion.

          With two colons before the MESSAGE, the words special array
          and the CURRENT special parameter are modified to refer only
          to the normal arguments when the ACTION is executed or
          evaluated.  With three colons before the MESSAGE they are
          modified to refer only to the normal arguments covered by
          this description.

    OPTSPEC
    OPTSPEC:...
          This describes an option.  The colon indicates handling for
          one or more arguments to the option; if it is not present,
          the option is assumed to take no arguments.

          By default, options are multi-character name, one `-WORD' per
          option.  With -s, options may be single characters, with more
          than one option per word, although words starting with two
          hyphens, such as `--prefix', are still considered complete
          option names.  This is suitable for standard GNU options.

          The combination of -s with -w allows single-letter options to
          be combined in a single word even if one or more of the
          options take arguments.  For example, if -a takes an
          argument, with no -s `-ab' is considered as a single
          (unhandled) option; with -s -ab is an option with the
          argument `b'; with both -s and -w, -ab may be the option -a
          and the option(-b) with arguments still to come.

          The option -W takes this a stage further:  it is possible to
          complete single-letter options even after an argument that
          occurs in the same word.  However, it depends on the action
          performed whether options will really be completed at this
          point.  For more control, use a utility function like _guard
          as part of the action.

          The following forms are available for the initial OPTSPEC,
          whether or not the option has arguments.

         *OPTSPEC
               Here OPTSPEC is one of the remaining forms below.  This
               indicates the following OPTSPEC may be repeated.
               Otherwise if the corresponding option is already present
               on the command line to the left of the cursor it will
               not be offered again.

         -OPTNAME
         +OPTNAME
               In the simplest form the OPTSPEC is just the option name
               beginning with a minus or a plus sign, such as `-foo'.
               The first argument for the option (if any) must follow
               as a _separate_ word directly after the option.

               Either of `-+OPTNAME' and `+-OPTNAME' can be used to
               specify that -OPTNAME and +OPTNAME are both valid.

               In all the remaining forms, the leading `-' may be
               replaced by or paired with `+' in this way.

         -OPTNAME-
               The first argument of the option must come directly
               after the option name _in the same word_.  For example,
               `-foo-:...' specifies that the completed option and
               argument will look like `-fooARG'.

         -OPTNAME+
               The first argument may appear immediately after OPTNAME
               in the same word, or may appear as a separate word after
               the option.  For example, `-foo+:...' specifies that the
               completed option and argument will look like either
               `-fooARG' or `-foo ARG'.

         -OPTNAME=
               The argument may appear as the next word, or in same
               word as the option name provided that it is separated
               from it by an equals sign, for example `-foo=ARG' or
               `-foo ARG'.

         -OPTNAME=-
               The argument to the option must appear after an equals
               sign in the same word, and may not be given in the next
               argument.

         OPTSPEC[EXPLANATION]
               An explanation string may be appended to any of the
               preceding forms of OPTSPEC by enclosing it in brackets,
               as in `-q[query operation]'.

               The verbose style is used to decide whether the
               explanation strings are displayed with the option in a
               completion listing.

               If no bracketed explanation string is given but the
               auto-description style is set and only one argument is
               described for this OPTSPEC, the value of the style is
               displayed, with any appearance of the sequence `%d' in
               it replaced by the MESSAGE of the first OPTARG that
               follows the OPTSPEC; see below.

          It is possible for options with a literal `+' or `=' to
          appear, but that character must be quoted, for example `-\+'.

          Each OPTARG following an OPTSPEC must take one of the
          following forms:

         :MESSAGE:ACTION
         ::MESSAGE:ACTION
               An argument to the option; MESSAGE and ACTION are
               treated as for ordinary arguments.  In the first form,
               the argument is mandatory, and in the second form it is
               optional.

               This group may be repeated for options which take
               multiple arguments.  In other words,
               :MESSAGE1:ACTION1:MESSAGE2:ACTION2 specifies that the
               option takes two arguments.

         :*PATTERN:MESSAGE:ACTION
         :*PATTERN::MESSAGE:ACTION
         :*PATTERN:::MESSAGE:ACTION
               This describes multiple arguments.  Only the last OPTARG
               for an option taking multiple arguments may be given in
               this form.  If the PATTERN is empty (i.e., :*:), all the
               remaining words on the line are to be completed as
               described by the ACTION; otherwise, all the words up to
               a word matching the PATTERN are to be completed using
               the ACTION.

               Multiple colons are treated as for the `*:...' forms for
               ordinary arguments:  when the MESSAGE is preceded by two
               colons, the words special array and the CURRENT special
               parameter are modified during the execution or
               evaluation of the ACTION to refer only to the words
               after the option.  When preceded by three colons, they
               are modified to refer only to the words covered by this
               description.

     Any literal colon in an OPTNAME, MESSAGE, or ACTION must be
     preceded by a backslash, `\:'.

     Each of the forms above may be preceded by a list in parentheses
     of option names and argument numbers.  If the given option is on
     the command line, the options and arguments indicated in
     parentheses will not be offered.  For example, `(-two -three
     1)-one:...' completes the option `-one'; if this appears on the
     command line, the options -two and -three and the first ordinary
     argument will not be completed after it.  `(-foo):...' specifies
     an ordinary argument completion; -foo will not be completed if
     that argument is already present.

     Other items may appear in the list of excluded options to indicate
     various other items that should not be applied when the current
     specification is matched: a single star (*) for the rest arguments
     (i.e. a specification of the form `*:...'); a colon (:) for all
     normal (non-option-) arguments; and a hyphen (-) for all options.
     For example, if `(*)' appears before an option and the option
     appears on the command line, the list of remaining arguments
     (those shown in the above table beginning with `*:') will not be
     completed.

     To aid in reuse of specifications, it is possible to precede any
     of the forms above with `!'; then the form will no longer be
     completed, although if the option or argument appears on the
     command line they will be skipped as normal.  The main use for
     this is when the arguments are given by an array, and _arguments
     is called repeatedly for more specific contexts: on the first call
     `_arguments $global_options' is used, and on subsequent calls
     `_arguments !$^global_options'.

     In each of the forms above the ACTION determines how completions
     should be generated.  Except for the `->STRING' form below, the
     ACTION will be executed by calling the _all_labels function to
     process all tag labels.  No special handling of tags is needed
     unless a function call introduces a new one.

     The forms for ACTION are as follows.

      (single unquoted space)
          This is useful where an argument is required but it is not
          possible or desirable to generate matches for it.  The
          MESSAGE will be displayed but no completions listed.  Note
          that even in this case the colon at the end of the MESSAGE is
          needed; it may only be omitted when neither a MESSAGE nor an
          ACTION is given.

    (ITEM1 ITEM2 ...)
          One of a list of possible matches, for example:

               :foo:(foo bar baz)

    ((ITEM1\:DESC1 ...))
          Similar to the above, but with descriptions for each possible
          match.  Note the backslash before the colon.  For example,

               :foo:((a\:bar b\:baz))

          The matches will be listed together with their descriptions
          if the description style is set with the values tag in the
          context.

    ->STRING
          In this form, _arguments processes the arguments and options
          and then returns control to the calling function with
          parameters set to indicate the state of processing; the
          calling function then makes its own arrangements for
          generating completions.  For example, functions that
          implement a state machine can use this type of action.

          Where _arguments encounters a `->STRING', it will strip all
          leading and trailing whitespace from STRING and set the array
          state to the set of all STRINGSs for which an action is to be
          performed.

          By default and in common with all other well behaved
          completion functions, _arguments returns zero if it was able
          to add matches and non-zero otherwise. However, if the -R
          option is given, _arguments will instead return a status of
          300 to indicate that $state is to be handled.

          In addition to $state, _arguments also sets the global
          parameters `context', `line' and `opt_args' as described
          below, and does not reset any changes made to the special
          parameters such as PREFIX and words.  This gives the calling
          function the choice of resetting these parameters or
          propagating changes in them.

          A function calling _arguments with at least one action
          containing a `->STRING' therefore must declare appropriate
          local parameters:

               local context state line
               typeset -A opt_args

          to avoid _arguments from altering the global environment.

    {EVAL-STRING}
          A string in braces is evaluated as shell code to generate
          matches.  If the EVAL-STRING itself does not begin with an
          opening parenthesis or brace it is split into separate words
          before execution.

    = ACTION
          If the ACTION starts with `= ' (an equals sign followed by a
          space), _arguments will insert the contents of the ARGUMENT
          field of the current context as the new first element in the
          words special array and increment the value of the CURRENT
          special parameter.  This has the effect of inserting a dummy
          word onto the completion command line while not changing the
          point at which completion is taking place.

          This is most useful with one of the specifiers that restrict
          the words on the command line on which the ACTION is to
          operate (the two- and three-colon forms above).  One
          particular use is when an ACTION itself causes _arguments on
          a restricted range; it is necessary to use this trick to
          insert an appropriate command name into the range for the
          second call to _arguments to be able to parse the line.

    WORD...
    WORD...
          This covers all forms other than those above.  If the ACTION
          starts with a space, the remaining list of words will be
          invoked unchanged.

          Otherwise it will be invoked with some extra strings placed
          after the first word; these are to be passed down as options
          to the compadd builtin.  They ensure that the state specified
          by _arguments, in particular the descriptions of options and
          arguments, is correctly passed to the completion command.
          These additional arguments are taken from the array parameter
          `expl'; this will be set up before executing the ACTION and
          hence may be referred to inside it, typically in an expansion
          of the form `$expl[@]' which preserves empty elements of the
          array.

     During the performance of the action the array `line' will be set
     to the command name and normal arguments from the command line,
     i.e. the words from the command line excluding all options and
     their arguments.  Options are stored in the associative array
     `opt_args' with option names as keys and their arguments as the
     values.  For options that have more than one argument these are
     given as one string, separated by colons.  All colons in the
     original arguments are preceded with backslashes.

     The parameter `context' is set when returning to the calling
     function to perform an action of the form `->STRING'.  It is set
     to an array of elements corresponding to the elements of $state.
     Each element is a suitable name for the argument field of the
     context: either a string of the form `option-OPT-N' for the N'th
     argument of the option -OPT, or a string of the form `argument-N'
     for the N'th argument.  For `rest' arguments, that is those in the
     list at the end not handled by position, N is the string `rest'.
     For example, when completing the argument of the -o option, the
     name is `option-o-1', while for the second normal (non-option-)
     argument it is `argument-2'.

     Furthermore, during the evaluation of the ACTION the context name
     in the curcontext parameter is altered to append the same string
     that is stored in the context parameter.

     It is possible to specify multiple sets of options and arguments
     with the sets separated by single hyphens.  The specifications
     before the first hyphen (if any) are shared by all the remaining
     sets.  The first word in every other set provides a name for the
     set which may appear in exclusion lists in specifications, either
     alone or before one of the possible values described above.  In
     the second case a `-' should appear between this name and the
     remainder.

     For example:

          _arguments \
              -a \
            - set1 \
              -c \
            - set2 \
              -d \
              ':arg:(x2 y2)'

     This defines two sets.  When the command line contains the option
     `-c', the `-d' option and the argument will not be considered
     possible completions.  When it contains `-d' or an argument, the
     option `-c' will not be considered.  However, after `-a' both sets
     will still be considered valid.

     If the name given for one of the mutually exclusive sets is of the
     form `(NAME)' then only one value from each set will ever be
     completed; more formally, all specifications are mutually
     exclusive to all other specifications in the same set.  This is
     useful for defining multiple sets of options which are mutually
     exclusive and in which the options are aliases for each other.  For
     example:

          _arguments \
              -a -b \
            - '(compress)' \
              {-c,--compress}'[compress]' \
            - '(uncompress)' \
              {-d,--decompress}'[decompress]'

     As the completion code has to parse the command line separately
     for each set this form of argument is slow and should only be used
     when necessary.  A useful alternative is often an option
     specification with rest-arguments (as in `-foo:*:...'); here the
     option -foo swallows up all remaining arguments as described by
     the OPTARG definitions.

     The options -S and -A are available to simplify the specifications
     for commands with standard option parsing.  With -S, no option
     will be completed after a `--' appearing on its own on the line;
     this argument will otherwise be ignored; hence in the line

          foobar -a -- -b

     the `-a' is considered an option but the `-b' is considered an
     argument, while the `--' is considered to be neither.

     With -A, no options will be completed after the first non-option
     argument on the line.  The -A must be followed by a pattern
     matching all strings which are not to be taken as arguments.  For
     example, to make _arguments stop completing options after the
     first normal argument, but ignoring all strings starting with a
     hyphen even if they are not described by one of the OPTSPECs, the
     form is `-A "-*"'.

     The option `-O NAME' specifies the name of an array whose elements
     will be passed as arguments to functions called to execute ACTIONS.
     For example, this can be used to pass the same set of options for
     the compadd builtin to all ACTIONs.

     The option `-M SPEC' sets a match specification to use to
     completion option names and values.  It must appear before the
     first argument specification.  The default is `r:|[_-]=* r:|=*':
     this allows partial word completion after `_' and `-', for example
     `-f-b' can be completed to `-foo-bar'.

     The option -C tells _arguments to modify the curcontext parameter
     for an action of the form `->STATE'.  This is the standard
     parameter used to keep track of the current context.  Here it (and
     not the context array) should be made local to the calling function
     to avoid passing back the modified value and should be initialised
     to the current value at the start of the function:

          local curcontext="$curcontext"

     This is useful where it is not possible for multiple states to be
     valid together.

     The option `-' allows _arguments to work out the names of long
     options that support the `--help' option which is standard in many
     GNU commands.  The command word is called with the argument
     `--help' and the output examined for option names.  Clearly, it can
     be dangerous to pass this to commands which may not support this
     option as the behaviour of the command is unspecified.

     In addition to options, `_arguments --' will try to deduce the
     types of arguments available for options when the form `--OPT=VAL'
     is valid.  It is also possible to provide hints by examining the
     help text of the command and adding specifiers of the form
     `PATTERN:MESSAGE:ACTION'; note that normal _arguments specifiers
     are not used.  The PATTERN is matched against the help text for an
     option, and if it matches the MESSAGE and ACTION are used as for
     other argument specifiers.  For example:

          _arguments -- '*\*:toggle:(yes no)' \
                        '*=FILE*:file:_files' \
                        '*=DIR*:directory:_files -/' \
                        '*=PATH*:directory:_files -/'

     Here, `yes' and `no' will be completed as the argument of options
     whose description ends in a star; file names will be completed for
     options that contain the substring `=FILE' in the description; and
     directories will be completed for options whose description
     contains `=DIR' or `=PATH'.  The last three are in fact the
     default and so need not be given explicitly, although it is
     possible to override the use of these patterns.  A typical help
     text which uses this feature is:

            -C, --directory=DIR          change to directory DIR

     so that the above specifications will cause directories to be
     completed after `-directory', though not after `-C'.

     Note also that _arguments tries to find out automatically if the
     argument for an option is optional.  This can be specified
     explicitly by doubling the colon before the MESSAGE.

     If the PATTERN ends in `(-)', this will removed from the pattern
     and the ACTION will be used only directly after the `=', not in
     the next word.  This is the behaviour of a normal specification
     defined with the form `=-'.

     The `_arguments --' can be followed by the option `-i PATTERNS' to
     give patterns for options which are not to be completed.  The
     patterns can be given as the name of an array parameter or as a
     literal list in parentheses.  For example,

          _arguments -- -i \
              "(--(en|dis)able-FEATURE*)"

     will cause completion to ignore the options `--enable-FEATURE' and
     `--disable-FEATURE' (this example is useful with GNU configure).

     The `_arguments --' form can also be followed by the option `-s
     PAIR' to describe option aliases.  Each PAIR consists of a pattern
     and a replacement.  For example, some configure-scripts describe
     options only as `--enable-foo', but also accept `--disable-foo'.
     To allow completion of the second form:

          _arguments -- -s "(#--enable- --disable-)"

     Here is a more general example of the use of _arguments:

          _arguments '-l+:left border:' \
                     '-format:paper size:(letter A4)' \
                     '*-copy:output file:_files::resolution:(300 600)' \
                     ':postscript file:_files -g \*.\(ps\|eps\)' \
                     '*:page number:'

     This describes three options: `-l', `-format', and `-copy'.  The
     first takes one argument described as `LEFT BORDER' for which no
     completion will be offered because of the empty action.  Its
     argument may come directly after the `-l' or it may be given as
     the next word on the line.

     The `-format' option takes one argument in the next word,
     described as `PAPER SIZE' for which only the strings `letter' and
     `A4' will be completed.

     The `-copy' option may appear more than once on the command line
     and takes two arguments.  The first is mandatory and will be
     completed as a filename.  The second is optional (because of the
     second colon before the description `RESOLUTION') and will be
     completed from the strings `300' and `600'.

     The last two descriptions say what should be completed as
     arguments.  The first describes the first argument as a
     `POSTSCRIPT FILE' and makes files ending in `ps' or `eps' be
     completed.  The last description gives all other arguments the
     description `PAGE NUMBERS' but does not offer completions.

_cache_invalid CACHE_IDENTIFIER
     This function returns status zero if the completions cache
     corresponding to the given cache identifier needs rebuilding.  It
     determines this by looking up the cache-policy style for the
     current context.  This should provide a function name which is run
     with the full path to the relevant cache file as the only argument.

     Example:

          _example_caching_policy () {
              # rebuild if cache is more than a week old
              oldp=( "$1"(Nmw+1) )
              (( $#oldp ))
          }

_call_function RETURN NAME [ ARGS ... ]
     If a function NAME exists, it is called with the arguments ARGS.
     The RETURN argument gives the name of a parameter in which the
     return status from the function NAME; if RETURN is empty or a
     single hyphen it is ignored.

     The return value of _call_function itself is zero if the function
     NAME exists and was called and non-zero otherwise.

_call_program TAG STRING ...
     This function provides a mechanism for the user to override the
     use of an external command.  It looks up the command style with
     the supplied TAG.  If the style is set, its value is used as the
     command to execute.  The STRINGs from the call to _call_program,
     or from the style if set, are concatenated with spaces between
     them and the resulting string is evaluated.  The return value is
     the return value of the command called.

_combination [ -s PATTERN ] TAG STYLE SPEC ... FIELD OPTS ...
     This function is used to complete combinations of values,  for
     example pairs of hostnames and usernames.  The STYLE argument
     gives the style which defines the pairs; it is looked up in a
     context with the TAG specified.

     The style name consists of field names separated by hyphens, for
     example `users-hosts-ports'.  For each field for a value is
     already known, a SPEC of the form `FIELD=PATTERN' is given.  For
     example, if the command line so far specifies a user `pws', the
     argument `users=pws' should appear.

     The next argument with no equals sign is taken as the name of the
     field for which completions should be generated (presumably not
     one of the FIELDs for which the value is known).

     The matches generated will be taken from the value of the style.
     These should contain the possible values for the combinations in
     the appropriate order (users, hosts, ports in the example above).
     The different fields the values for the different fields are
     separated by colons.  This can be altered with the option -s to
     _combination which specifies a pattern.  Typically this is a
     character class, as for example `-s "[:@]"' in the case of the
     users-hosts style.    Each `FIELD=PATTERN' specification restricts
     the completions which apply to elements of the style with
     appropriately matching fields.

     If no style with the given name is defined for the given tag, or
     if none of the strings in style's value match, but a function name
     of the required field preceded by an underscore is defined, that
     function will be called to generate the matches.  For example, if
     there is no `users-hosts-ports' or no matching hostname when a
     host is required, the function `_hosts' will automatically be
     called.

     If the same name is used for more than one field, in both the
     `FIELD=PATTERN' and the argument that gives the name of the field
     to be completed, the number of the field (starting with one) may
     be given after the fieldname, separated from it by a colon.

     All arguments after the required field name are passed to compadd
     when generating matches from the style value, or to the functions
     for the fields if they are called.

_describe [ -oO | -t TAG ] DESCR NAME1 [ NAME2 ] OPTS ... -- ...
     This function associates completions with descriptions.  Multiple
     groups separated by -- can be supplied, potentially with different
     completion options OPTS.

     The DESCR is taken as a string to display above the matches if the
     format style for the descriptions tag is set.  This is followed by
     one or two names of arrays followed by options to pass to compadd.
     The first array contains the possible completions with their
     descriptions in the form `COMPLETION:DESCRIPTION'.  If a second
     array is given, it should have the same number of elements as the
     first; in this case the corresponding elements are added as
     possible completions instead of the COMPLETION strings from the
     first array.  The completion list will retain the descriptions
     from the first array.  Finally, a set of completion options can
     appear.

     If the option `-o' appears before the first argument, the matches
     added will be treated as names of command options (N.B. not shell
     options), typically following a `-', `--' or `+' on the command
     line.  In this case _describe uses the prefix-hidden,
     prefix-needed and verbose styles to find out if the strings should
     be added as completions and if the descriptions should be shown.
     Without the `-o' option, only the verbose style is used to decide
     how descriptions are shown.  If `-O' is used instead of `-O',
     command options are completed as above but _describe will not
     handle the prefix-needed style.

     With the -t option a TAG can be specified.  The default is
     `values' or, if the -o option is given, `options'.

     If selected by the list-grouped style, strings with the same
     description will appear together in the list.

     _describe uses the _all_labels function to generate the matches, so
     it does not need to appear inside a loop over tag labels.

_description [ -x ] [ -12VJ ] TAG NAME DESCR [ SPEC ... ]
     This function is not to be confused with the previous one; it is
     used as a helper function for creating options to compadd.  It is
     buried inside many of the higher level completion functions and so
     often does not need to be called directly.

     The styles listed below are tested in the current context using the
     given TAG.  The resulting options for compadd are put into the
     array named NAME (this is traditionally `expl', but this
     convention is not enforced).  The description for the
     corresponding set of matches is passed to the function in DESCR.

     The styles tested are: format, hidden, matcher, ignored-patterns
     and group-name.  The format style is first tested for the given
     TAG and then for the descriptions tag if no value was found, while
     the remainder are only tested for the tag given as the first
     argument.  The function also calls _setup which tests some more
     styles.

     The string returned by the format style (if any) will be modified
     so that the sequence `%d' is replaced by the DESCR given as the
     third argument without any leading or trailing white space.  If,
     after removing the white space, the DESCR is the empty string, the
     format style will not be used and the options put into the NAME
     array will not contain an explanation string to be displayed above
     the matches.

     If _description is called with more than three arguments, the
     additional SPECs should be of the form `CHAR:STR'.  These supply
     escape sequence replacements for the format style: every
     appearance of `%CHAR' will be replaced by STRING.

     If the -x option is given, the description will be passed to
     compadd using the -x option instead of the default -X.  This means
     that the description will be displayed even if there are no
     corresponding matches.

     The options placed in the array NAME take account of the
     group-name style, so matches are placed in a separate group where
     necessary.  The group normally has its elements sorted (by passing
     the option -J to compadd), but if an option starting with `-V',
     `-J', `-1', or `-2' is passed to _description, that option will be
     included in the array.  Hence it is possible for the completion
     group to be unsorted by giving the option `-V', `-1V', or `-2V'.

     In most cases, the function will be used like this:

          local expl
          _description files expl file
          compadd "$expl[@]" - "$files[@]"

     Note the use of the parameter expl, the hyphen, and the list of
     matches.  Almost all calls to compadd within the completion system
     use a similar format; this ensures that user-specified styles are
     correctly passed down to the builtins which implement the
     internals of completion.

_dispatch CONTEXT STRING ...
     This sets the current context to CONTEXT and looks for completion
     functions to handle this context by hunting through the list of
     command names or special contexts (as described above for compdef)
     given as STRING ....  The first completion function to be defined
     for one of the contexts in the list is used to generate matches.
     Typically, the last STRING is -default- to cause the function for
     default completion to be used as a fallback.

     The function sets the parameter $service to the STRING being
     tried, and sets the CONTEXT/COMMAND field (the fourth) of the
     $curcontext parameter to the CONTEXT given as the first argument.

_files
     The function _files calls _path_files with all the arguments it
     was passed except for -g and -/.  The use of these two options
     depends on the setting of the  file-patterns style.

     This function accepts the full set of options allowed by
     _path_files, described below.

_gnu_generic
     This function is a simple wrapper around the _arguments function
     described above.  It can be used to determine automatically the
     long options understood by commands that produce a list when
     passed the option `--help'.  It is intended to be used as a
     top-level completion function in its own right.  For example, to
     enable option completion for the commands foo and bar, use

          compdef _gnu_generic foo bar

     after the call to compinit.

     The completion system as supplied is conservative in its use of
     this function, since it is important to be sure the command
     understands the option `-'-help'.

_guard [ OPTIONS ] PATTERN DESCR
     This function is intended to be used in the ACTION for the
     specifications passed to _arguments and similar functions.  It
     returns immediately with a non-zero return value if the string to
     be completed does not match the PATTERN.  If the pattern matches,
     the DESCR is displayed; the function then returns zero if the word
     to complete is not empty, non-zero otherwise.

     The PATTERN may be preceded by any of the options understood by
     compadd that are passed down from _description, namely -M, -J, -V,
     -1, -2, -n, -F and -X.  All of these options will be ignored.
     This fits in conveniently with the argument-passing conventions of
     actions for _arguments.

     As an example, consider a command taking the options -n and -none,
     where -n must be followed by a numeric value in the same word.  By
     using:

          _argument '-n-: :_guard "[0-9]#" "numeric value"' '-none'

     _arguments can be made to both display the message `numeric value'
     and complete options after `-n<TAB>'.  If the `-n' is already
     followed by one or more digits (the pattern passed to _guard) only
     the message will be displayed; if the `-n' is followed by another
     character, only options are completed.

_message [ -r12 ] [ -VJ GROUP ] DESCR
_message -e [ TAG ] DESCR
     The DESCR is used in the same way as the third argument to the
     _description function, except that the resulting string will
     always be shown whether or not matches were generated.  This is
     useful for displaying a help message in places where no
     completions can be generated.

     The format style is examined with the messages tag to find a
     message; the usual tag, descriptions, is used only if the style is
     not set with the former.

     If the -r option is given, no style is used; the DESCR is taken
     literally as the string to display.  This is most useful when the
     DESCR comes from a pre-processed argument list which already
     contains an expanded description.

     The -12VJ options and the GROUP are passed to compadd and hence
     determine the group the message string is added to.

     The second form gives a description for completions with the tag
     TAG to be shown even if there are no matches for that tag.  The tag
     can be omitted and if so the tag is taken from the parameter
     $curtag; this is maintained by the completion system and so is
     usually correct.

_multi_parts SEP ARRAY
     The argument SEP is a separator character.  The ARRAY may be
     either the name of an array parameter or a literal array in the
     form `(foo bar)', a parenthesised list of words separated by
     whitespace.  The possible completions are the strings from the
     array.  However, each chunk delimited by SEP will be completed
     separately.  For example, the _tar function uses `_multi_parts /
     PATHARRAY' to complete partial file paths from the given array of
     complete file paths.

     The -i option causes _multi_parts to insert a unique match even if
     that requires multiple separators to be inserted.  This is not
     usually the expected behaviour with filenames, but certain other
     types of completion, for example those with a fixed set of
     possibilities, may be more suited to this form.

     Like other utility functions, this function accepts the `-V',
     `-J', `-1', `-2', `-n', `-f', `-X', `-M', `-P', `-S', `-r', `-R',
     and `-q' options and passes them to the compadd builtin.

_next_label [ -x ] [ -12VJ ] TAG NAME DESCR [ OPTIONS ... ]
     This function is used to implement the loop over different tag
     labels for a particular tag as described above for the tag-order
     style.  On each call it checks to see if there are any more tag
     labels; if there is it returns status zero, otherwise non-zero.
     As this function requires a current tag to be set, it must always
     follow a call to _tags or _requested.

     The -x12VJ options and the first three arguments are passed to the
     _description function.  Where appropriate the TAG will be replaced
     by a tag label in this call.  Any description given in the
     tag-order style is preferred to the DESCR passed to _next_label.

     The OPTIONS given after the DESCR are set in the parameter given
     by NAME, and hence are to be passed to compadd or whatever
     function is called to add the matches.

     Here is a typical use of this function for the tag foo.  The call
     to _requested determines if tag foo is required at all; the loop
     over _next_label handles any labels defined for the tag in the
     tag-order style.

          local expl ret=1
          ...
          if _requested foo; then
            ...
            while _next_label foo expl '...'; do
              compadd "$expl[@]" ... && ret=0
            done
            ...
          fi
          return ret

_normal
     This is the standard function called to handle completion outside
     any special -CONTEXT-.  It is called both to complete the command
     word and also the arguments for a command.  In the second case,
     _normal looks for a special completion for that command, and if
     there is none it uses the completion for the -default- context.

     A second use is to reexamine the command line specified by the
     $words array and the $CURRENT parameter after those have been
     modified.  For example, the function _precommand, which completes
     after pre-command specifiers such as nohup, removes the first word
     from the words array, decrements the CURRENT parameter, then calls
     _normal again.  The effect is that `nohup CMD ...'  is treated in
     the same way as `CMD ...'.

     If the command name matches one of the patterns given by one of the
     options -p or -P to compdef, the corresponding completion function
     is called and then the parameter _compskip is checked.  If it is
     set completion is terminated at that point even if no matches have
     been found.  This is the same effect as in the -first- context.

_options
     This can be used to complete the names of shell options.  It
     provides a matcher specification that ignores a leading `no',
     ignores underscores and allows upper-case letters to match their
     lower-case counterparts (for example, `glob', `noglob', `NO_GLOB'
     are all completed).  Any arguments are propagated to the compadd
     builtin.

_options_set and _options_unset
     These functions complete only set or unset options, with the same
     matching specification used in the _options function.

     Note that you need to uncomment a few lines in the _main_complete
     function for these functions to work properly.  The lines in
     question are used to store the option settings in effect before
     the completion widget locally sets the options it needs.  Hence
     these functions are not generally used by the completion system.

_parameters
     This is used to complete the names of shell parameters.

     The option `-g PATTERN' limits the completion to parameters whose
     type matches the PATTERN.  The type of a parameter is that shown
     by `print ${(t)PARAM}', hence judicious use of `*' in PATTERN is
     probably necessary.

     All other arguments are passed to the compadd builtin.

_path_files
     This function is used throughout the completion system to complete
     filenames.  It allows completion of partial paths.  For example,
     the string `/u/i/s/sig' may be completed to
     `/usr/include/sys/signal.h'.

     The options accepted by both _path_files and _files are:

    -f
          Complete all filenames.  This is the default.

    -/
          Specifies that only directories should be completed.

    -g PATTERN
          Specifies that only files matching the PATTERN should be
          completed.

    -W PATHS
          Specifies path prefixes that are to be prepended to the
          string from the command line to generate the filenames but
          that should not be inserted as completions nor shown in
          completion listings.  Here, PATHS may be the name of an array
          parameter, a literal list of paths enclosed in parentheses or
          an absolute pathname.

    -F IGNORED-FILES
          This behaves as for the corresponding option to the compadd
          builtin.  It gives direct control over which filenames should
          be ignored.  If the option is not present, the
          ignored-patterns style is used.

     Both _path_files and _files also accept the following options
     which are passed to compadd: `-J', `-V', `-1', `-2', `-n', `-X',
     `-M', `-P', `-S', `-q', `-r', and `-R'.

     Finally, the _path_files function  uses the styles expand,
     ambiguous, special-dirs, list-suffixes and file-sort described
     above.

_pick_variant [ -c COMMAND ] [ -r NAME ] LABEL=PATTERN ... LABEL [ ARGS ... ]
     This function is used to resolve situations where a single command
     name requires more than one type of handling, either because it
     has more than one variant or because there is a name clash between
     two different commands.

     The command to run is taken from the first element of the array
     words unless this is overridden by the option -c.  This command is
     run and its output is compared with a series of patterns.
     Arguments to be passed to the command can be specified at the end
     after all the other arguments.  The patterns to try in order are
     given by the arguments LABEL=PATTERN; if the output of `COMMAND
     ARGS ...' contains PATTERN, then label is selected as the label
     for the command variant.  If none of the patterns match, the final
     command label is selected and status 1 is returned.

     If the `-r NAME' is given, the LABEL picked is stored in the
     parameter named NAME.

     The results are also cached in the _CMD_VARIANT associative array
     indexed by the name of the command run.

_regex_arguments NAME SPEC ...
     This function generates a completion function NAME which matches
     the specifications SPEC ..., a set of regular expressions as
     described below.  After running _regex_arguments, the function
     NAME should be called at the appropriate point.  The pattern to be
     matched is given by the contents of the words array up to the
     current cursor position joined together with null characters; no
     quotation is applied.

     The arguments are grouped as sets of alternatives separated by `|',
     which are tried one after the other until one matches.  Each
     alternative consists of a one or more specifications which are
     tried left to right, with each pattern matched being stripped in
     turn from the command line being tested, until all of the group
     succeeds or until one fails; in the latter case, the next
     alternative is tried.  This structure can be repeated to arbitrary
     depth by using parentheses; matching proceeds from inside to
     outside.

     A special procedure is applied if no test succeeds but the
     remaining command line string contains no null character (implying
     the remaining word is the one for which completions are to be
     generated).  The completion target is restricted to the remaining
     word and any ACTIONs for the corresponding patterns are executed.
     In this case, nothing is stripped from the command line string.
     The order of evaluation of the ACTIONs can be determined by the
     tag-order style; the various formats supported by _alternative can
     be used in ACTION.  The DESCR is used for setting up the array
     parameter expl.

     Specification arguments take one of following forms, in which
     metacharacters such as `(', `)', `#' and `|' should be quoted.

    /PATTERN/ [%LOOKAHEAD%] [-GUARD] [:TAG:DESCR:ACTION]
          This is a single primitive component.  The function tests
          whether the combined pattern `(#b)((#B)PATTERN)LOOKAHEAD*'
          matches the command line string.  If so, `GUARD' is evaluated
          and its return status is examined to determine if the test
          has succeeded.  The PATTERN string `[]' is guaranteed never
          to match.  The LOOKAHEAD is not stripped from the command
          line before the next pattern is examined.

    /PATTERN/+ [%LOOKAHEAD%] [-GUARD] [:TAG:DESCR:ACTION]
          This is similar to `/PATTERN/ ...' but the left part of the
          command line string (i.e. the part already matched by
          previous patterns) is also considered part of the completion
          target.

    /PATTERN/- [%LOOKAHEAD%] [-GUARD] [:TAG:DESCR:ACTION]
          This is similar to `/PATTERN/ ...' but the ACTIONs of the
          current and previously matched patterns are ignored even if
          the following `PATTERN' matches the empty string.

    ( SPEC )
          Parentheses may be used to groups SPECs; note each parenthesis
          is a single argument to _regex_arguments.

    SPEC #
          This allows any number of repetitions of SPEC.

    SPEC SPEC
          The two SPECs are to be matched one after the other as
          described above.

    SPEC | SPEC
          Either of the two SPECs can be matched.

_requested [ -x ] [ -12VJ ] TAG [ NAME DESCR [ COMMAND ARGS ... ] ]
     This function is called to decide whether a tag already registered
     by a call to _tags (see below) has been requested by the user and
     hence completion should be performed for it.  It returns status
     zero if the tag is requested and non-zero otherwise.  The function
     is typically used as part of a loop over different tags as follows:

          _tags foo bar baz
          while _tags; do
            if _requested foo; then
              ... # perform completion for foo
            fi
            ... # test the tags bar and baz in the same way
            ... # exit loop if matches were generated
          done

     Note that the test for whether matches were generated is not
     performed until the end of the _tags loop.  This is so that the
     user can set the tag-order style to specify a set of tags to be
     completed at the same time.

     If NAME and DESCR are given, _requested calls the _description
     function with these arguments together with the options passed to
     _requested.

     If COMMAND is given, the _all_labels function will be called
     immediately with the same arguments.  In simple cases this makes it
     possible to perform the test for the tag and the matching in one
     go.  For example:

          local expl ret=1
          _tags foo bar baz
          while _tags; do
            _requested foo expl 'description' \
                compadd foobar foobaz && ret=0
            ...
            (( ret )) || break
          done

     If the COMMAND is not compadd, it must nevertheless be prepared to
     handle the same options.

_retrieve_cache CACHE_IDENTIFIER
     This function retrieves completion information from the file given
     by CACHE_IDENTIFIER, stored in a directory specified by the
     cache-path style which defaults to ~/.zsh/cache.  The return value
     is zero if retrieval was successful.  It will only attempt
     retrieval if the use-cache style is set, so you can call this
     function without worrying about whether the user wanted to use the
     caching layer.

     See _store_cache below for more details.

_sep_parts
     This function is passed alternating arrays and separators as
     arguments.  The arrays specify completions for parts of strings to
     be separated by the separators.  The arrays may be the names of
     array parameters or a quoted list of words in parentheses.  For
     example, with the array `hosts=(ftp news)' the call `_sep_parts
     '(foo bar)' @ hosts' will complete the string  `f' to `foo' and
     the string `b@n' to `bar@news'.

     This function accepts the compadd options `-V', `-J', `-1', `-2',
     `-n', `-X', `-M', `-P', `-S', `-r', `-R', and `-q' and passes them
     on to the compadd builtin used to add the matches.

_setup TAG [ GROUP ]
     This function sets up the special parameters used by the
     completion system appropriately for the TAG given as the first
     argument.  It uses the styles list-colors, list-packed,
     list-rows-first, last-prompt, accept-exact, menu and force-list.

     The optional GROUP supplies the name of the group in which the
     matches will be placed.  If it is not given, the TAG is used as
     the group name.

     This function is called automatically from _description and hence
     is not normally called explicitly.

_store_cache CACHE_IDENTIFIER PARAMS ...
     This function, together with _retrieve_cache and _cache_invalid,
     implements a caching layer which can be used in any completion
     function.  Data obtained by costly operations are stored in
     parameters; this function then dumps the values of those
     parameters to a file.  The data can then be retrieved quickly from
     that file via _retrieve_cache, even in different instances of the
     shell.

     The CACHE_IDENTIFIER specifies the file which the data should be
     dumped to.  The file is stored in a directory specified by the
     cache-path style which defaults to ~/.zsh/cache.  The remaining
     PARAMS arguments are the parameters to dump to the file.

     The return value is zero if storage was successful.  The function
     will only attempt storage if the use-cache style is set, so you can
     call this function without worrying about whether the user wanted
     to use the caching layer.

     The completion function may avoid calling _retrieve_cache when it
     already has the completion data available as parameters.  However,
     in that case it should call _cache_invalid to check whether the
     data in the parameters and in the cache are still valid.

     See the _perl_modules completion function for a simple example of
     the usage of the caching layer.

_tags [ [ -C NAME ] TAGS ... ]
     If called with arguments, these are taken to be the names of tags
     valid for completions in the current context.  These tags are
     stored internally and sorted by using the tag-order style.

     Next, _tags is called repeatedly without arguments from the same
     completion function.  This successively selects the first, second,
     etc. set of tags requested by the user.  The return value is zero
     if at least one of the tags is requested and non-zero otherwise.
     To test if a particular tag is to be tried, the _requested
     function should be called (see above).

     If `-C NAME' is given, NAME is temporarily stored in the argument
     field (the fifth) of the context in the curcontext parameter
     during the call to _tags; the field is restored on exit.  This
     allows _tags to use a more specific context without having to
     change and reset the curcontext parameter (which has the same
     effect).

_values [ -O NAME ] [ -s SEP ] [ -S SEP ] [ -wC ] DESC SPEC ...
     This is used to complete arbitrary keywords (values) and their
     arguments, or lists of such combinations.

     If the first argument is the option `-O NAME', it will be used in
     the same way as by the _arguments function.  In other words, the
     elements of the NAME array will be passed to compadd when
     executing an action.

     If the first argument (or the first argument after `-O NAME') is
     `-s', the next argument is used as the character that separates
     multiple values.  This character is automatically added after each
     value in an auto-removable fashion (see below); all values
     completed by `_values -s' appear in the same word on the command
     line, unlike completion using _arguments.  If this option is not
     present, only a single value will be completed per word.

     Normally, _values will only use the current word to determine
     which values are already present on the command line and hence are
     not to be completed again.  If the -w option is given, other
     arguments are examined as well.

     The first non-option argument is used as a string to print as a
     description before listing the values.

     All other arguments describe the possible values and their
     arguments in the same format used for the description of options by
     the _arguments function (see above).  The only differences are that
     no minus or plus sign is required at the beginning, values can
     have only one argument, and the forms of action beginning with an
     equal sign are not supported.

     The character separating a value from its argument can be set
     using the option -S (like -s, followed by the character to use as
     the separator in the next argument).  By default the equals sign
     will be used as the separator between values and arguments.

     Example:

          _values -s , 'description' \
                  '*foo[bar]' \
                  '(two)*one[number]:first count:' \
                  'two[another number]::second count:(1 2 3)'

     This describes three possible values: `foo', `one', and `two'.
     The first is described as `bar', takes no argument and may appear
     more than once.  The second is described as `number', may appear
     more than once, and takes one mandatory argument described as
     `first count'; no action is specified, so it will not be
     completed.  The `(two)' at the beginning says that if the value
     `one' is on the line, the value `two' will no longer be considered
     a possible completion.  Finally, the last value (`two') is
     described as `another number' and takes an optional argument
     described as `second count' for which the completions (to appear
     after an `=') are `1', `2', and `3'.  The _values function will
     complete lists of these values separated by commas.

     Like _arguments, this function temporarily adds another context
     name component to the arguments element (the fifth) of the current
     context while executing the ACTION.  Here this name is just the
     name of the value for which the argument is completed.

     The style verbose is used to decide if the descriptions for the
     values (but not those for the arguments) should be printed.

     The associative array val_args is used to report values and their
     arguments; this works similarly to the opt_args associative array
     used by _arguments.  Hence the function calling _values should
     declare the local parameters state, line, context and val_args:

          local context state line
          typeset -A val_args

     when using an action of the form `->STRING'.  With this function
     the context parameter will be set to the name of the value whose
     argument is to be completed.

     Note also that _values normally adds the character used as the
     separator between values as an auto-removable suffix (similar to a
     `/' after a directory).  However, this is not possible for a
     `->STRING' action as the matches for the argument are generated by
     the calling function.  To get the usual behaviour, the the calling
     function can add the separator X as a suffix by passing the
     options `-qS X' either directly or indirectly to compadd.

     The option -C is treated in the same way as it is by _arguments.
     In that case the parameter curcontext should be made local instead
     of context (as described above).

_wanted [ -x ] [ -C NAME ]  [ -12VJ ] TAG NAME DESCR COMMAND ARGS ...
     In many contexts, completion can only generate one particular set
     of matches, usually corresponding to a single tag.  However, it is
     still necessary to decide whether the user requires matches of
     this type.  This function is useful in such a case.

     The arguments to _wanted are the same as those to _requested, i.e.
     arguments to be passed to _description.  However, in this case the
     COMMAND is not optional;  all the processing of tags, including
     the loop over both tags and tag labels and the generation of
     matches, is carried out automatically by _wanted.

     Hence to offer only one tag and immediately add the corresponding
     matches with the given description:

          _wanted tag expl 'description' \
              compadd matches...

     Note that, as for _requested, the COMMAND must be able to accept
     options to be passed down to compadd.

     Like _tags this function supports the -C option to give a
     different name for the argument context field.  The -x option has
     the same meaning as for _description.

