-------------------------------------
CHANGES FROM PREVIOUS VERSIONS OF ZSH
-------------------------------------

Note also the list of incompatibilities in the README file.

Changes since 5.8.1
-------------------

zsh 5.9 is dedicated to the memory of Sven Guckes, who was, amongst other
things, a long-time zsh advocate.  For more information, see:

  https://linuxnews.de/2022/02/sven-guckes-verstorben/
  https://groups.google.com/g/vim_announce/c/MJBKVd-xrEE/m/joVNaDgAAgAJ

When unsetting a hash element, the string enclosed in square brackets is
interpreted literally after any normal command-line-argument expansions.
Thus
  unset "hash[$key]"
first expands $key as usual for a double-quoted string, and then interprets
that result as the exact hash element to unset.  This differs from previous
versions of the shell, which would also remove a leading backslash for an
unusual subset of characters in the expansion of $key.  Note this also
means, for example, that now
  unset 'hash[ab]cd]'
unsets the element with key "ab]cd" rather than silently doing nothing.

The function command learnt a -T option to declare a function and enable
tracing for it simultaneously.

The option SHORT_REPEAT was added to enable the short syntax of
SHORT_LOOPS for the repeat command only. It is disabled by default.

The _arguments function now supports NUL-delimiting optargs in the
opt_args array via the -0 option. Developers of completion functions
should find this easier to handle reliably than the default
colon-delimiting behaviour.

The zsh/system module's `zsystem flock` command learnt an -i option to
set the wait interval used with -t. Additionally, -t now supports
fractional seconds.

The option CLOBBER_EMPTY was added to enable the overwrite behaviour
of CLOBBER for empty files only. It is disabled by default.

A (-) expansion flag was added. It works like (n) but correctly sorts
negative numbers.

The (*) expansion flag enables EXTENDED_GLOB for pattern matching.
For example, ${(*)sample/(#b)*(pat)*/${match[1]}} uses backreferences
even if EXTENDED_GLOB is not otherwise set.  However, this does not
descend into nested exapansions, and doubling as (**) does not disable
EXTENDED_GLOB.

The compinit function learnt a -w option to explain why compdump runs.
When run without the -i or -u options and compaudit discovers security
issues, answering "y" to the "Ignore insecure ..." prompt removes the
insecure elements (like the -i option) where previously it ignored the
result (thus formerly like the -u option).  Further, removing those
elements includes dropping directories from the $fpath array.

The zsh/datetime module's strftime builtin learnt an -n option to omit
the trailing newline when printing a formatted time.

The XTRACE option is now disabled while running user-defined completion
widgets.  This corresponds to long-standing behavior of other user ZLE
widgets.  Use the _complete_debug widget to capture XTRACE output, or
use "functions -T" to enable tracing of specific completion functions.

The fc builtin learnt an -s option which is a POSIX equivalent to the
`fc -e-` method of re-executing a command without invoking an editor.

The option CASE_PATHS was added to control how NO_CASE_GLOB behaves.
NO_CASE_GLOB + NO_CASE_PATHS is equivalent to the current NO_CASE_GLOB
behaviour. NO_CASE_GLOB + CASE_PATHS treats only path components that
contain globbing characters as case-insensitive; this behaviour may
yield more predictable results on case-sensitive file systems.
NO_CASE_PATHS is the default.

With the new TYPESET_TO_UNSET option set, "typeset foo" leaves foo unset,
in contrast to the default behavior which assigns foo="".  Any parameter
attributes such as numeric type, sorting, and padding are retained until
the parameter is explicitly unset or a conflicting value is assigned.
This is similar to default behavior of bash and ksh.  This option is
disabled by default.

The compadd builtin's -D option can now be specified more than once.

The zsh/zutil module's zformat builtin learnt an -F option which behaves
like -f except that ternary expressions check for existence instead of
doing math evaluation.

The conventional syntax used to indicate units, ranges, and default values
in completion descriptions (e.g. `timeout (seconds) (0-60) [20]`) is now
recognised by the completion system itself. These components are parsed
out of the description and can be individually styled. A _numbers helper
function has been added to help function authors offer rich completion
for these values.

The log builtin, WATCH parameter, et al., have been broken out into a
separate module, zsh/watch. The module is enabled by default.

The zsh/watch module's WATCHFMT parameter now supports colours via the
%F and %K escapes.

The STTY parameter can now be set to an empty string before running a
command to automatically restore terminal settings after the command
finishes.

The "jobs" command and "$jobstates" and related parameters can report on
parent shell jobs even in subshells.  This is a snapshot of the parent
state, frozen at the point the subshell started.  However, if a subshell
starts its own background jobs, the parent state is discarded in order
to report on those new jobs.

Changes from 5.8 to 5.8.1
-------------------------

CVE-2021-45444: Some prompt expansion sequences, such as %F, support
'arguments' which are themselves expanded in case they contain colour
values, etc. This additional expansion would trigger PROMPT_SUBST
evaluation, if enabled. This could be abused to execute code the user
didn't expect. e.g., given a certain prompt configuration, an attacker
could trick a user into executing arbitrary code by having them check
out a Git branch with a specially crafted name.

This is fixed in the shell itself by no longer performing PROMPT_SUBST
evaluation on these prompt-expansion arguments.

Users who are concerned about an exploit but unable to update their
binaries may apply the partial work-around described in the file
Etc/CVE-2021-45444-VCS_Info-workaround.patch included with the shell
source. [ Reported by RyotaK <security@ryotak.me>. Additional thanks to
Marc Cornellà <hello@mcornella.com>. ]

A regression was introduced in 5.8.1 in which, when reading a script
from standard input, zsh itself would consume lines that should otherwise
have been consumed by commands executed earlier in the script. This was
not intentional and has been fixed in subsequent versions.

Changes from 5.7.1-test-3 to 5.8
--------------------------------

CVE-2019-20044: When unsetting the PRIVILEGED option, the shell sets its
effective user and group IDs to match their respective real IDs. On some
platforms (including Linux and macOS, but not FreeBSD), when the RUID and
EUID were both non-zero, it was possible to regain the shell's former
privileges by e.g. assigning to the EUID or EGID parameter. In the course
of investigating this issue, it was also found that the setopt built-in
did not correctly report errors when unsetting the option, which
prevented users from handling them as the documentation recommended.
setopt now returns non-zero if it is unable to safely drop privileges.
[ Reported by Sam Foxman <samfoxman320@gmail.com>. ]

Changes from 5.7.1 to 5.7.1-test-3
----------------------------------

The zsh/zutil module's zparseopts builtin learnt an -F option to abort
parsing when an unrecognised option-like parameter is encountered.

The zsh/files module gained a chmod builtin.

Several changes have been made to the way completion functions track
'precommands' (such as `command` and `env`) and determine whether the
command being completed for is a shell builtin. Developers of completion
functions may wish to familiarise themselves with `_normal -p` and
`_pick_variant -b`.

The option CD_SILENT was added to suppress all output from cd (whether
explicit or implicit with AUTO_CD). It is disabled by default.

The compadd builtin's -o option now takes an optional argument to
specify the order of completion matches. This affects the display
of candidate matches and the order in which they are selected when
cycling between them using menu completion.

The :h and :t modifiers in parameter expansion (if braces are present),
glob qualifiers and history expansion may take following decimal digit
arguments in order to keep that many leading or trailing path components
instead of the defaults of all but one (:h) and one (:t).  In an absolute
path the leading '/' counts as one component.

The functions builtin gained a -c option to efficiently copy functions.

The zshmisc(1) manual page incorrectly stated that when 'exit' is used
in a `try' block inside a function, the corresponding `always' block will
be executed.  The manual page has been corrected.  The shell's behaviour
has not changed, but code such as the following:
.
    f() { { exit } always { echo Hello world } }
.
should be changed either to use 'return' instead of 'exit', or to have
the try/always block outside of any function.

Changes from 5.6.2 to 5.7.1
---------------------------

There are only minor changes between 5.7 and 5.7.1.

Support for 24-bit true color terminals has been added. Hex triplets
can be used when specifying colours for prompts and line editor
highlighting. On 88 and 256 colour terminals, a new zsh/nearcolor module
allows colours specified with hex triplets to be matched against the
nearest available colour.

The zsh/datetime module's strftime builtin now accepts an argument
specifying the nanoseconds time component; both arguments can be omitted
to use the current time.

Changes from 5.6.1 to 5.6.2
---------------------------

Fix another SIGTTOU case.

Fix SIGWINCH being ignored when zsh is not in the foreground.

The release tarballs are now compressed using xz(1), whereas previously
both xz(1) and gzip(1) versions were available.  If this gets in your way,
give us a shout.

Changes from 5.6 to 5.6.1
-------------------------

Fix packaging issue that broke runhelp.

Fix a regression with pipelines getting backgrounded and emitting SIGTTOU.

Changes from 5.5.1-test-2 to 5.6
--------------------------------

CVE-2018-0502: Data from the second line of a #! script file might be passed to
execve().  For example, in the following situation -
.
    printf '#!foo\nbar' > baz
    ./baz
.
the shell might take "bar" rather than "foo" for the argv[0] to be passed to
execve().  [ Reported by Anthony Sottile and Buck Evan. ]

CVE-2018-13259: A shebang line longer than 64 characters would be truncated.
For example, in the following situation:
.
    ( printf '#!'; repeat 64 printf 'x'; printf 'y' ) > foo
    ./foo
.
the shell might execute x...x (64 repetitions) rather than x...xy (64 x's,
one y).  [ Reported by Daniel Shahaf. ]

Changes from 5.5.1 to 5.5.1-test-2
----------------------------------

Non-stop IEEE 754 arithmetic support - Inf and NaN are now returned
from floating point operations where errors were printed before.
Inf and NaN are also recognised in arithmetic expressions.

In shell patterns, [[:blank:]] now honours the locale instead of
matching exclusively on space and tab, like for the other POSIX
character classes or for extended regular expressions.

The zsh/system module now provides the PID of the last process
substitution via $sysparams[procsubstpid].

Time formatting via the %D prompt escape now offers nanosecond
precision with the %. and %N format specifiers. Additionally,
nanosecond precision on file times is supported in the module
zsh/stat.

The zsh/mathfunc module now includes a log2() function.

The parameter ZLE_RECURSIVE has been added to indicate the
current ZLE recursion level.

Changes from 5.5 to 5.5.1
-------------------------

Apart from a fix for a configuration problem finding signal names from
(some) recent versions of glibc, there are only minor changes.

Changes from 5.4.2 to 5.5
-------------------------

The effect of the NO_INTERACTIVE_COMMENTS option extends into $(...) and
`...` command substitutions when used on the command line.  Previously,
comments were always recognized within command substitutions unless the
comment character "#" was disabled via reset of $histchars.

An alternative assignment syntax for indicating indices for arrays
and keys for associative arrays:

typeset -a array=([1]=first [2]=second)
typeset -A assoc=([key1]=val1 [key2]=val2)

is allowed for compatibility with other shells.  In the case of normal
arrays the new syntax can be mixed with the old.

The %E, %S, and %U TIMEFMT specifiers now support m and u prefixes
(e.g., %mE) to output times in milliseconds and microseconds,
respectively.

The option CHECK_RUNNING_JOBS was added to control whether zsh should
check for running jobs in addition to suspended ones with CHECK_JOBS.
It is enabled by default.

Changes from 5.3.1 to 5.4.2
---------------------------

There are only minor changes between 5.4 and 5.4.2.

The 'exec' and 'command' precommand modifiers, and options to them, are
now parsed after parameter expansion.  Previously, both the modifier and
any options to it were parsed between alias expansion and parameter
expansion (see zshexpn(1)), so they could neither be quoted nor be the
result of parameter expansion.  Examples: 's=command; $s -V ls' and
'\command -V ls' now work as expected.

Functions executed by ZLE widgets no longer have their standard input
closed, but redirected from /dev/null instead. That still guards
against user defined widgets inadvertently reading from the tty device.

There is an option WARN_NESTED_VAR, a companion to the existing
WARN_CREATE_GLOBAL that causes a warning if a function updates a
variable from an enclosing scope without using typeset -g.  It can be
turned on for an individual function with "functions -W".

zmodload now has an option -s to be silent on a failure to find a module
but still print other errors.

The autoload builtin gained several new features to load functions from a
file path determined at the time of definition rather than at the time of
loading.

The zsh/parameter module now exposes the file paths associated with
shell functions via the parameters functions_source and
dis_functions_source.

Changes from 5.2 to 5.3.1
-------------------------

There are only minor compatibility fixes between 5.3 and 5.3.1.

It is possible to enable character width support for Unicode 9 by
configuring with `--enable-unicode9'; this compiles in some additional
tables.  At some point this support may move into a module, in which
case the configure option will be changed to cause the module to be
permanently loaded.  This option is not useful unless your terminal also
supports Unicode 9.

The new word modifier ':P' computes the physical path of the argument.
It is different from the existing ':a' modifier which always resolves
'/before/here/../after' to '/before/after', and differs from the
existing ':A' modifier which resolves symlinks only after 'here/..' is
removed, even when /before/here is itself a symbolic link.  It is
recommended to review uses of ':A' and, if appropriate, convert them
to ':P' as soon as compatibility with 5.2 is no longer a requirement.

The output of "typeset -p" uses "export" commands or the "-g" option
for parameters that are not local to the current scope.  Previously,
all output was in the form of "typeset" commands, never using "-g".

vi-repeat-change can repeat user-defined widgets if the widget calls
zle -f vichange.

The parameter $registers now makes the contents of vi register buffers
available to user-defined widgets.

New vi-up-case and vi-down-case builtin widgets bound to gU/gu (or U/u
in visual mode) for doing case conversion.

A new select-word-match function provides vim-style text objects with
configurable word boundaries using the existing match-words-by-style
mechanism.

Support for the conditional expression [[ -v var ]] to test if a
variable is set for compatibility with other shells.

The print and printf builtins have a new option -v to assign the output
to a variable. This is for bash compatibility but with the additional
feature that, for an array, a separate element is used each time the
format is reused.

New x: syntax in completion match specifications make it possible to
disable match specifications hardcoded in completion functions.

Changes from 5.1.1 to 5.2
-------------------------

The new module zsh/param/private can be loaded to allow the shell
to define parameters that are private to a function scope (i.e. are
not propagated to nested functions called within this function).

The parameter flag ${(P)...} is now more useful when it appears in
a nested expansion.  For example,

  typeset -A assoc=(one un two deux three trois)
  name=assoc
  print ${${(P)name}[one]}

now prints "un".  In previous versions of the shell the value of the
substitution was fully expanded on return from ${(P)name}, making
associative array subscripting difficult.  As a side effect, flags
for formatting appearing in the inner substitution now affect the
substitution of the name (into "assoc" in this case), which is not
normally useful: flags that should apply to the value must be in the
outer substitution.

The GLOB_STAR_SHORT option allows the pattern **/* to be shortened to
just ** if no / follows. so **.c searches recursively for a file whose
name has the suffix ".c".

The effect of the WARN_CREATE_GLOBAL option has been significantly
extended, so expect it to cause additional warning messages about
parameters created globally within function scope.

Paste highlighting (added in 5.1) is now enabled by default to signal
that accept-line hasn't occurred.  Paste highlighting may be disabled
via
  zle_highlight+=(paste:none)
.  Disabling paste highlighting will retain the "bracketed paste"
behaviour, unless that is separately disabled via zle_bracketed_paste.

Changes from 5.1 to 5.1.1
-------------------------

5.1.1 is primarily a bug fix release; however, a few minor features were
added.

The ZLE variables YANK_ACTIVE, YANK_START and YANK_END have been added
and are useful for managing highlighting.

The zsh-specific pattern match range tests have been supplemented with
[:INCOMPLETE:] and [:INVALID:] to help detect the state of partially
read multibyte character strings.

Changes from 5.0.8 to 5.1
-------------------------

The builtins declare, export, local, readonly and typeset
now have corresponding reserved words.  When used in
this form, the builtin syntax is extended so that assignments
following the reserved word are treated similarly to
assignments that appear at the start of the command line.
For example,
  local scalar=`echo one word` array=(several words)
creates a local "scalar" containing the text "one word"
and an array "array" containing the words "several"
"words".

- The print builtin has new options -x and -X to expand tabs.

- Several new command completions and numerous updates to others.

- Options to "fc" to segregate internal and shared history.

- All emulations including "sh" use multibyte by default; several
  repairs to multibyte handling.

- ZLE supports "bracketed paste" mode to avoid interpreting pasted
  newlines as accept-line.  Pastes can be highlighted for visibility
  and to make it more obvious whether accept-line has occurred.

- Improved (though still not perfect) POSIX compatibility for getopts
  builtin when POSIX_BUILTINS is set.

- New setopt APPEND_CREATE for POSIX-compatible NO_CLOBBER behaviour.

- Completion of date values now displays in a calendar format when
  the complist module is available.  Controllable by zstyle.

- New parameter UNDO_LIMIT_NO for more control over ZLE undo repeat.

- Several repairs/improvements to the contributed narrow-to-region
  ZLE function.

- Many changes to child-process and signal handling to eliminate race
  conditions and avoid deadlocks on descriptor and memory management.

- New builtin sysopen in zsh/system module for detailed control of
  file descriptor modes.


Changes from 5.0.0 to 5.0.8
---------------------------

- Global aliases can be created for syntactic tokens such as command
  separators (";", "&", "|", "&&", "||"), redirection operators, etc.
  Use at your own risk!  The POSIX_ALIASES option is interpreted more
  strictly to prevent expansion of these and other alias names containing
  quotes, glob metacharacters, parameter references, etc.

- There have been various further improvements to builtin handling
  with the POSIX_BUILTINS option (off by default) for compatibility with
  the POSIX standard.

- 'whence -v' is now more informative, and 'whence -S' shows you
  how a full chain of symbolic links resolves to a command.

- The 'p' parameter flag now allows an argument to be specified
  as a reference to a variable, e.g. ${(ps.$sep.)foo} to split $foo
  on a string given by $sep.

- The option FORCE_FLOAT now forces variables, not just constants,
  to floating point in arithmetic expressions.

- The type of an assignment in arithmetic expressions, e.g. the
  type seen by the variable res in $(( res = a = b )), is now
  more logical and C-like.

- The default binding of 'u' in vi command mode has changed to undo
  multiple changes when invoked repeatedly. '^R' is now bound to redo
  changes. To revert to toggling of the last edit use:
    bindkey -a u vi-undo-change

- Compatibility with Vim has been improved for vi editing mode. Most
  notably, Vim style text objects are supported and the region can be
  manipulated with vi commands in the same manner as Vim's visual mode.

- Elements of the watch variable may now be patterns.

- The logic for retrying history locking has been improved.

- Some rationalisations have been made to the zsh/db/gdbm module that
  should make it more useful and predictable in operation.

- Numeric constants encountered in mathematical expressions (but not other
  contexts) can contain underscores as separators that will be ignored on
  evaluation, as allowed in other scripting languages.  For example,
  0xFFFF_FFFF, or 3.141_592_654.  From 5.0.6 this is also available
  in output, e.g.
    setopt cbases
    zmodload zsh/mathfunc
    print $(( [#16_4] 2**32 - 1 )) $(( [#_3] 4 * atan(1.0) ))

- "functions -T" turns on tracing for the specified function(s) only,
  similar to "functions -t" except that tracing is turned off for any
  functions called from the specified one(s) that don't also have the -t
  or -T flag.

- The option FORCE_FLOAT has been added to force all arithmetic constants
  to be treated as floating point.  This is most useful locally within
  functions or scripts performing floating point calculations.

- The default $fpath/$FPATH is now designed to include
  /usr/local/share/zsh/site-functions unless the installer has
  specifically decided to use another path, i.e. regardless of
  the standard installation location.  This directory does not need to
  exist.  Sites that set an explicit site directory can put that in
  /etc/zshenv as before.  The intention of the new path element is to
  increase the likelihood that locally added functions can be found with
  the shell running "out of the box", unless the shell has been
  deliberately configured differently by the installer for some special
  purpose.

- Individual pattern characters can be disabled.  For example, to allow '^'
  to be an ordinary character even if the option EXTENDED_GLOB is set, use
  "disable -p '^'".

- The variable editing builtin vared can be given custom editing widgets
  for initialisation and finishing.

- The line editor's capability for listening on file descriptors
  additional to the terminal has been enhanced so that the handler for
  such file descriptors can be a line editor widget.  Previously the
  handler always behaved as a standard shell function.

- Hooks for adding history (the function zshaddhistory and the
  array zshaddhistory_functions) can return status 2 to indicate that
  history is to be saved internally within the shell but not written.

- In file completion, the recursive-files style can be set to an array of
  patterns to match against "$PWD/".  In any matched location, it is
  possible to complete files in arbitrarily deep subdirectories without
  needing to type the directory prefix.  See example in the zshcompsys
  manual.

- The _user_expand completer now allows expansion functions in the
  user-expand files to return a string in REPLY that will be used to name
  the set of expansions returned.

- The parameter HISTORY_IGNORE may be set to a pattern which matches
  lines in the internal history that are to be omitted from the history
  file at file write time.  This differs from history changes made in
  the zshaddhistory hook or by the HIST_IGNORE_* options, all of which
  take effect immediately on the internal history list itself.

- The parameter ZLE_RPROMPT_INDENT can be set to 0 to remove the space
  before the right hand side of the screen (this causes problems with
  some terminals).  It is not special and is not set by default; the
  effect in that case is as if it was 1, as in previous versions.

- If the option EXTENDED_GLOB is in effect, it is possible to force
  globbing within conditional code using the [[ ... ]] syntax by flagging
  that a certain string is a glob using the (#q) glob qualifier syntax.
  The resulting glob is treated as a single argument.  For example,
  [[ -n *.c(#qN) ]] tests whether there are any .c files in the current
  directory.

- In prompt strings, the %N(l.true.false) conditional (line length) and
  the %N<..< and %N>..> truncation operators now accept negative values
  of N, which count the remaining space to the opposite margin (positive
  values of N still count the space used since the start of the prompt).
  In PS1 and PROMPT, this counts to the right margin, whereas in RPS1 and
  RPROMPT, it counts to the left margin (not to the opposite prompt).

- Also in prompt strings, %e or the equivalent test %(e..) are used to
  output or test the execution / evaluation depth of a shell
  construct within functions etc.  This is useful in $PS4.

- Another new prompt feature is the %. escape within time strings, for
  example %D{%H:%M:%S.%.}.  It provides zero-padded decimal fractions of a
  second; by default milliseconds are shown, but the number of digits may
  be indicated from 1 to 6, e.g. "%6.".  (Note this is part of the
  extensions to strftime() formats rather than basic prompt escapes.)

- The operators :^ and :^^ in parameter substitution allow for array
  zipping in the form ${name:^array}. With the :^ operator, all entries
  in $name and $array will be output in alternating order. With :^ the
  longer array is trimmed whereas the :^^ operator repeats the shorter
  array enough to match the longer array.

- The value of $? when a job becomes stopped is now the signal number plus
  128, for compatibility with other shells.  Note that different operating
  systems use different values e.g. for SIGTSTP, so it is not possible in
  portable scripts to detect stopped jobs by comparing to a fixed number.
  Also, the value of $pipestatus is now updated when a job stops, not just
  when it exits.

- Redirections applied to function definitions take effect when the
  function is executed, not when it is defined.  Other shells already
  work this way.  For example,
    fn() { echo hello } >~/logfile
  Running fn writes "hello" to logfile.  In older versions of the shell
  it would create an empty file at the point of definition.

Changes between 4.2 and 5.0.0
-----------------------------

The following changes first appeared in the 4.3 series of releases;
see also the file Etc/NEWS-4.3.

Here is a summary of the most significant changes:

- Multibyte characters strings are supported throughout the shell.
  Various options, editor features, and expansion flags have been
  added to aid in using them.

- The following new options have appeared: COMBINING_CHARS,
  DEBUG_BEFORE_CMD, HASH_EXECUTABLES_ONLY, HIST_FCNTL_LOCK,
  HIST_LEX_WORDS, HIST_SAVE_BY_COPY, MULTIBYTE, NO_MULTI_FUNCDEF,
  PATH_SCRIPT, POSIX_ALIASES, POSIX_CD, POSIX_JOBS, POSIX_STRINGS,
  POSIX_TRAPS, PROMPT_SP, SOURCE_TRACE.

- Highlighting and colouring of the command line is supported.

- Job control is supported in non-interactive shells and subshells.

- The zshroadmap manual page provides a slightly more helpful
  introduction to the shell manual than was previously available.

- There have been some notable enhancements to POSIX compatibility
  when the shell is in a corresponding emulation (e.g. "emulate sh").

Expansion (parameters, globbing, etc.) and redirection
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

- The character group tests [[:IDENT:]], [[:IFS:]], [[:IFSSPACE:]],
  [[:WORD:]] in patterns allow testing if a character can be
  part of an identifier, is an IFS character, is an IFS whitespace
  character, or is considered part of the word using the line editor's
  logic based on the shell variable WORDCHARS.

- In extended globbing, "(#cN,M)" means "match the preceding group
  at least N but no more than M times".

- The glob qualifier P can be used with an argument to add an extra
  word before each glob match.

- The syntax ~[...] provides dynamic directory naming by means
  of the shell function zsh_directory_name or associated hook functions.
  This is useful for expanding paths with many variable components as
  commonly found in software development.

- Parameter substitution has the ${NAME:OFFSET} and ${NAME:OFFSET:LENGTH}
  syntax for compatibility with other shells (and zero-based indexing
  is used to enhance compatibility).  LENGTH may be negative to count
  from the end.

- The arbitrary limit on parameter subscripts (262144) has been removed.
  As it was not configurable and tested in an inconvenient place it
  was deemed preferable to remove it completely.  The limit was originally
  introduced to prevent accidental creation of a large parameter array
  by typos that generated assignments along the lines of "12345678=0".
  The general advice is not to do that.

- The parameter substitution flag (D) abbreviates directories in parameters
  using the familiar ~ form.

- The parameter substitution flag (g) can take delimited arguments o, e and
  c to provide echo- and print-style expansion: (g::) provides basic
  echo-style expansion; (g:e:) provides the extended capabilities of
  print; (g:o:) provides octal escapes without a leading zero; (g:c:)
  additionally expands "^c" style control characters as for bindkey.
  Options may be combined, e.g. (g:eoc:).

- The parameter substitution flag (m) indicates that string lengths used
  calculated by the (l) and (r) flags or the # operator should take
  account of the printing width of characters in multibyte mode, whether
  0, 1 or more.  (mm) causes printing characters to count as 1 and
  non-printing characters to count as 0.

- The parameter substitution flag (q-) picks the most minimal way of
  quoting the parameter words, to make the result as readable as possible.

- The parameter substitution flag (Z), a variant of (z), takes arguments
  describing how to split a variable using shell syntax: (Z:c:) parses
  comments as strings (the default is not to treat comment characters
  specially); (Z:C:) parses comments and strips them; (Z:n:) treats
  newlines as ordinary whitespace (the default is to turn unquoted
  newlines into semicolons; this is now documented).

- The parameter subscript flag (e) forces the argument to be treated
  as a string, never a pattern, e.g. ${array[(ie)*]} looks for the
  index of the array element containing the literal string "*".

- The operators :| and :* in parameter substitution allow for array
  subtraction and intersection in the form ${name:|array}. With the :|
  operator, all entries in $name that are also in $array will be removed
  from the substitution. Conversely for the :* operation only the
  entries that are in both arrays will be substituted.

- Numeric expansions can have a positive or negative step
  e.g. "{3..9..2}".  Negative start and end of ranges are also now
  supported.

- =(<<<...) is optimised to eliminate the need for an external process.
  It writes the given string to a file and substitutes the name on the
  command line.

- The redirection operations "{myfd}>file" and "{myfd}>&-" open and
  close a new file descriptor (at least 10) contained in the shell
  variable myfd, which can be written to with ">&$myfd".  This allows
  arbitrary file descriptors rather than the explicit range 0 to 9.

- New prompt escapes:
  %x and %I show source file and line number, useful in $PS4 (the
    existing %N and %i show names and lines in the execution environment
    rather than the source file).
  %F, %K, %f, %k allow colouring of prompts both using ANSI colour names
    and values supported by individual terminal emulators.

Builtins and shell functions
-+-+-+-+-+-+-+-+-+-+-+-+-+-+

- Directory-changing builtins take an option -q to suppress side
  effects such as printing directories or calling the chpwd hook functions.

- Various enhancements have been made to traps:
  - The option DEBUG_BEFORE_CMD is on by default, so DEBUG traps
    can be used to debug code about to be run
  - $ZSH_DEBUG_CMD in such a trap gives the code to be run
  - "setopt ERR_EXIT" in a DEBUG trap causes the code not to be executed

- The "fc" builtin is now more useful non-interactively.

Shell variables (parameters)
-+-+-+-+-+-+-+-+-+-+-+-+-+-+

- New variables:
  CORRECT_IGNORE can be set to a pattern to be ignored in spelling correction.
  KEYBOARD_HACK defines characters to be ignored if typed unmatched at
    the end of the line (an extension of the SUN_KEYBOARD_HACK option,
    but note that setting the option will override the variable).
  ZSH_PATCHLEVEL provides a unique indication of the code compiled to
    make the shell, even between releases.
  ZSH_SUBSHELL indicates the subshell level, incremented once per fork, at
    which the code is being run.

Options
-+-+-+-

- New options:
  COMBINING_CHARS: assume that the terminal displays combining
    characters correctly.  The shell cannot determine this by itself,
    hence the option.  This is highly recommended for MacOS X where
    file names are stored with accented characters split into basic
    and combining characters.
  DEBUG_BEFORE_CMD (on by default): execute debug traps before the
    code they refer to.  This is a change of the default behaviour
    as the new behaviour is much more useful.
  HASH_EXECUTABLES_ONLY: don't insert non-executable files into the
    command hash used e.g. by completion; this is optional as the
    resulting behaviour may be very slow on network paths.
  HIST_FCNTL_LOCK: Use the system's file locking mechanism instead
    of an ad-hoc mechanism for locking history files.
  HIST_LEX_WORDS: Perform lexical analysis on history lines read from
    files, so the words are more accurately determined.  May be very slow.
  HIST_SAVE_BY_COPY (on by default): if unset, write a history file in
    place by truncating the old one.  Only needs to be turned off in
    special circumstances.
  MULTIBYTE (on by default if available): both variables and editor
    command lines are treated as sequences of multibyte characters
    rather than raw bytes depending on the locale.  May be turned off
    within functions to perform bytewise operations.
  MULTI_FUNCDEF (on by default): "foo bar () { ... }" defines two
    functions.  This is often found to be confusing and bug-prone,
    so you may want to unset it.
  PATH_SCRIPT: search the path for a script specified as the first
    argument to the shell on invocation.
  POSIX_ALIASES: reserved words are not candidates for alias expansion.
  POSIX_CD: make directory changing more POSIX-compatible.
  POSIX_JOBS: make job control more POSIX compliant.
  POSIX_STRINGS: $'...\0...' always processes \0 as a NULL, but if the
    option is set the remainder of the string is ignored.
  POSIX_TRAPS: EXIT traps are not executed on return from shell functions.
  PROMPT_SP: improves display of lines not ending with newlines when
    PROMPT_CR is in effect.
  SOURCE_TRACE: print information as files are executed with ".",
    "source", or as startup or shutdown files.

Line editor
-+-+-+-+-+-

- Supports multibyte characters, including characters wider than one
  screen cell and (with the COMBINING_CHARS option) combining characters.

- New builtin widgets:
  arguments-base: allow non-decimal numeric arguments
  history-incremental-pattern-search-{backward,forward}: support
    patterns in incremental searches.

- New special variables:
  region_highlight allows arbitrary highlighting of parts of the
    command line; it is maintained dynamically.
  UNDO_CHANGE_NO gives a unique record of the current change state of
    the command line, for undoing back to a particular point using
    the undo widget.
  zle_highlight provides master control of highlighting for special
    modes, e.g. unprintable characters.
  ZLE_LINE_ABORTED records an editor line that was aborted by an error
    or C-g.  It can be used to recover aborted lines.
  ZLE_STATE give miscellaneous information, currently whether the line
    editor is in insert or overwrite mode.

- The undo widget takes an argument, a previous value of $UNDO_CHANGE_NO.

Completion
-+-+-+-+-+

- Many new and enhanced completion functions

- New styles:
  accept-exact-dirs:  suppress path expansion of directory components
    that already exist, speeding up completion significantly on slow
    network directories.
  path-completion:  can be used to suppress directory components before
    the current one completely, so e.g. /u/b<TAB> only completes after the
    "b", not the "u".

- New special variables:
  ZLE_REMOVE_SUFFIX_CHARS, ZLE_SPACE_SUFFIX_CHARS provide enhanced
    flexibility over suffix removal.

- Matching control, typically handled with the matcher-list style,
  supports named character ranges, such as [:upper:], wherever
  ranges were allowed, for example 'm:{[:upper:]}={[:lower:]}'.
  However, matching control does not yet handle multibyte characters
  properly, so this is currently limited to ASCII.

Syntax and compatibility
-+-+-+-+-+-+-+-+-+-+-+-+

- Substitutions of the form ${var:-"$@"} and ${var:+"$@"} now behave
  much more like other shells when appropriate (e.g. with the
  SH_WORD_SPLIT option).

- Assignments within variable substitutions, such as ${var=value},
  are also more compatible with other shells where appropriate.

- The emulate command can now be passed an expression to be evaluated
  in a "sticky" emulation, so that functions defined there always
  behave in the appropriate emulation.

- "emulate sh" and similar modes have improved compatibility with
  respect to deciding whether the shell should exit on errors.

- Signals now accept SIG as part of the name.

Modules
-+-+-+-

- Modules now present "features", specific builtins (b:), parameters
  (p:), conditions (c:) and math functions (f:), allowing more control
  over what is imported from a module.

- The zsh/curses module provides access to the "curses" screen
  manipulation package.

- The zsh/datetime module has a calendar utility, although it is not
  as robust as standalone calendar utilities.

- The zsh/newuser module and associated functions has facilities for
  setting up startup files for a first-time user.

- The zsh/parameter module contains some new arrays to aid in tracing
  of the shell's call stack: $funcsourcetrace and $funcfiletrace.

- The zsh/parameter module provides $usergroups, an associative arrays
  whose keys are the names of groups the current user belongs to, with
  the group identifier as the corresponding value.

- The zsh/system module has a zsystem builtin which provides file
  locking and also a forward-compatible means for testing subcommands
  supported.

Internal improvements
-+-+-+-+-+-+-+-+-+-+-

- High resolution timestamps are used internally for certain
  comparisons when available.

Add-on functions
-+-+-+-+-+-+-+-+

- The VCS_Info system provides a way of keeping track of the state
  of numerous version control systems within the shell.

- cdr etc.: change to a directory from a list that persists between
  shell instances, with completion support.

- regexp-replace replaces text in variables using regular expressions;
  it may be used by zle function widgets based on the functions
  replace-string and replace-string-again to provide regular expression
  replacements in the line editor.


Changes in 4.2 since version 4.2.0
----------------------------------

- The autoload and related builtins take options -k and -z to indicate
  ksh or zsh autoloading style for given functions, making it possible
  to mix and match.

- Assignments to associative arrays can use the i and r index flags.
  For example,
    assoc[(i)alpha*]=bravo
  sets the value for the element whose key matches the pattern `alpha*';
    assoc[(r)activ*]=passive
  sets the value for the element whose current value matches the pattern
  `activ*'.

- The glob qualifier F indicates a non-empty directory.  Hence *(F)
  indicates all subdirectories with entries, *(/^F) means all
  subdirectories with no entries.

- fc -p and fc -P provide push/pop for the status of the shell's
  history (both internal and using the history file).  With automatic
  scoping (fc -ap) it becomes easy to use a temporary history in a
  function.  This has been added to the calculator function zcalc to make
  its internal history work more seamlessly.

- A new `try block' and `always block' syntax has been introduced
  to make it easier to ensure the shell runs important tidy-up code
  in the event of an error.  It also runs after a break, continue, or
  return, including a return forced by the ERR_RETURN option
  (but not an exit, which is immediate).  The syntax is:
    `{' try-block-list `}' `always' `{' always-block-list `}'
  where no newline or semicolon may appear between `}' and `always'.
  This is compatible with all previous valid zsh syntax as an `always'
  at that point used to be a syntax error.  For example,
    { echo Code run in current shell } always { echo Tidy-up code }

- A new zle widget reset-prompt has been added to re-expand the current
  prompt.  Changes to the variable in use as well as changes in its
  expansions are both taken into account.  The same effect is now forced by
  a job change notification, making the %j prompt escape and %(j..) ternary
  expression more useful.

- The zftp module supports ports following the hostname in the normal suffix
  notation, `host:port'.  This requires IPv6 colon-style addresses to be
  specified in suitably quoted square brackets, for example:

  zftp open '[f000::baaa]'
  zftp open '[f000::baaa]:ftp'

  (the two are equivalent).

- Special traps, those that don't correspond to signals, i.e. ZERR, DEBUG
  and EXIT are no longer executed inside other traps.  This caused
  unnecessary confusion if, for example, both DEBUG and EXIT traps
  were set.  The new behaviour is more compatible with other shells.

- New option TRAPS_ASYNC which if set allows traps to run while the
  shell is waiting for a child process.  This is the traditional zsh
  behaviour; POSIX requires the option to be unset.  In sh/ksh
  compatibility mode the option is turned off by default and the option
  letter -T turns it on, for compatibility with FreeBSD sh.

- New WIDGETSTYLE, WIDGETFUNC parameters in ZLE.

- Glob qualifier (+func) is shorthand for (e:func:) (calls a command,
  typically a shell function, with no argument).


New features between zsh versions 4.0 and 4.2
---------------------------------------------

Configuration:
- upgraded to use autoconf post-2.50
- improved compatibility with other shells through shell options,
  builtin arguments and improved builtin option parsing

Syntax and builtins:
- new printf builtin
- `+=' to append to parameters which works for scalars, arrays and (with
  pairs) associative arrays.
- enhanced multiple parameter `for' loops:
    for key value in key1 value1 key2 value2 ...
  maintaining full compatibility with POSIX syntax.
- Suffix aliases allow the shell to run a command on a file by suffix,
  e.g `alias -s ps=gv' makes `foo.ps' execute `gv foo.ps'.  Supplied
  function zsh-mime-setup uses existing mailcap and mime.types files
  to set up suitable aliases.  Supplied function pick-web-browser is
  suitable for finding a browser to show .html etc. files by suffix alias.
- new option `no_case_glob' for case-insensitive globbing.

Add-on modules and functions:
- zsh/datetime modules makes date formatting and seconds since EPOCH
  available inside the shell.
- zsh/net/tcp module provides builtin interface to TCP through ztcp
  builtin.  Function suite for interactive and script use with expect-style
  pattern matching.
- zsh/net/socket module provides zsocket builtin.
- zcalc calculator function with full line editing.
- builtin interface to pcre library
- zsh/zselect module provides zselect builtin as interface to select
  system call

Completion system:
- general improvements to command and context support, low-level functions,
  display code.
- in verbose mode, matches with the same description are grouped
- highly configurable completions for values of specific parameters,
  specific redirections for specific commands
- support for bash completion functions (typically zsh native functions are
  more powerful where available)
- New completions provided for (some of these may be in later 4.0
  releases):  valgrind, tidy, texinfo, infocmp, Java classes, larch, limit,
  locale parameters, netcat, mysqldiff, mt, lsof, elinks, ant, debchange
  (dch), email addresses, file system types, Perforce, xsltproc.
  Plus many others.

Line editor:
- special parameters $PREDISPLAY, $POSTDISPLAY available in function
  widgets to configure uneditable text (for narrowing)
- recursive editing
- supplied widgets read-from-minibuffer, replace-string use these features
  (more intuitive prompting and argument reading than 4.0)
- access to killed text via $CUTBUFFER and $killring
- supplied highly configurable word widgets forward-word-match etc., can
  set what constitutes a word interactively or in startup script
  (implement bash-style behaviour, replacing previous bash-* word widgets)
- interface to incremental search via $LASTSEARCH
- better handling of keymaps in zle and widgets
- better support for output from user-defined widgets while zle is active
- tetris game which runs entirely in zle
- several other contributed widgets

Local internal improvements:
- disowned jobs are automatically restarted
- \u and \U print escapes for Unicode
- read -d <delimiter> allows a custom line ending.
- read -t <timeout>.
- line numbers in error messages and $PS4 output are more consistent
- `=prog' expands only paths, no longer aliases for consistency
- job display in prompts; `jobs' command output can be piped
- prompts: new $RPROMPT2, %^, %j, %y, enhanced %{, %}, %_.
- rand48() function in zsh/mathfunc for better randomness in arithmetic
  (if the corresponding math library function is present)
- $SECONDS parameter can be made floating point via `typeset -F SECONDS'
  for better timing accuracy
- improvements to command line history mechanism
- job table is dynamically sized, preventing overflow (typically seen
  previously in complex completions).
- many bugfixes


New features in zsh version 4.0.1
---------------------------------

Compared with 3.1.9, there are mostly incremental improvements to
  - the new completion system --- more functions, completers, styles...
  - the line editor
  - handling of signals and traps
  - the configuration system, particularly for modules
  - Cygwin support (now essentially complete)
  - arithmetic evaluation
  - the zpty (pseudoterminal handling) module
  - the test suite
plus various bug fixes and compatibility improvements.

The alias modules (zle.so as an alias for zsh/zle.so, etc.) have been
removed; use `zmodload -A' to load modules under other names.  This is
irrelevant if you are upgrading from 3.0.

Compared with the 3.0 series of releases (the last stable set), the most
significant of a large number of improvements in the shell are:
  - Dynamically loadable modules with hierarchical naming system
  - Shell functions as editor functions, with much additional builtin support
  - Incredibly rich new completion system; just needs a single
    initialization command to provide completion for all sorts of commands
    and contexts
  - Associative arrays
  - Lots of new features in parameter substitution and globbing; more
    logical handling of nested parameter substitutions
  - Rewritten pattern-matching (globbing) code supports approximate
    and case-insensitive matching and backreferences
  - Various custom modules for pty's, FTP, special parameters, etc.
  - Rewrites of many internal parts of the code: execution code to
    provide compilation to internal representation, pattern matching
  - Floating point arithmetic and mathematical functions module
  - A test suite
  - Various new options for compatibility with this, that and the other
See the 3.1.x changes below for more detail.


New features in zsh version 3.1.8 and 3.1.9
-------------------------------------------
These are primarily bug-fix versions.  There are only a few user-visible
changes.
 - Array slices ${array[a,b]} with b < a now correctly have zero length.


New features in zsh version 3.1.7
---------------------------------
Further enhancements to new completion system:
 - Comprehensive context-sensitive configuration via `styles', which
   can be set by the menu-driven front end in compinstall
 - General mechanism for setting patterns to be ignored in a completion;
   overriding  of patterns to be matched for functions
 - New completers: _prefix to complete word before cursor, _ignored
   to complete using words so far ignored (like $fignore but more
   powerful), _history to complete words from shell history
 - Multiple use of completers with different options, similarly splitting
   of different types of completion (`tags') so they are considered with
   different styles
 - Many more supplied completions for standard commands which work out of
   the box, and better handling of command line options/arguments which
   behave in the usual way
 - $fpath now set up to use installed functions by default; functions
   can be loaded just by `autoload -U compinit; compinit'
 - Much improved handling of nested quoting and nested braces
 - New LIST_PACKED and LIST_ROWS_FIRST completion options and corresponding
   styles
 - compctl library separated out (frozen but still supported)
 - User-friendly introduction available at zsh website
   http://zsh.sourceforge.net/

Additions to complist listing library (coloured completion and menu
selection):
 - Listings can be shown page by page (are by default for new completion)
 - Menu selection allows full up and down scrolling of long lists

Other editing features:
 - new parameters $PENDING, $MARK, $BUFFERLINES
 - Easy display of a prompt from within an editing widget

Code parsing, storing and execution:
 - Completely new system of storing code internally, greatly optimised
 - Much less memory for shell functions etc.
 - Can compile shell functions to .zwc `wordcode' functions for fast
   loading
 - Can create `digest' files of entire directories in .zwc format

Parameters:
 - Floating point support added, similar to ksh93, `typeset -F' and
   `typeset -E' declare floating point variables; usual C/Fortran-like
   rules for integer/float conversion
 - Mathematical library zsh/mathfunc contains all the standard mathematical
   functions for use in arithmetical expressions
 - Improved parsing of arithmetical expressions and better error messages
 - Special parameters can be made local
 - `typeset -h' hides specialness of parameters, either as parameter
   attribute or when declaring new local variable
 - Local parameters can now be exported as in other shells; new option
   GLOBAL_EXPORTS on by default provides old behaviour that `typeset -x'
   referred to global parameters.
 - zsh/parameter module enhanced: now needed for new completion; parameters
   provided have `-h' flag set so that they are hidden by `typeset', so
   that existing functions don't need to be changed
 - Quotes can be stripped from parameter values with ${(Q)...}, providing
   reverse of ${(q...)...} facility

Globbing and pattern matching:
 - Pattern matching rewritten for efficiency
 - Supports `backreferences', i.e. extracting parenthesised chunks of
   matches, e.g.
     [[ $foo = (#b)(*/)[^/]* ]]
   stores the part of $foo up to the last / in $match[1] and the indexes of
   the match in $mbegin[1], $mend[1].  (#m) is also available to set $MATCH
   to the entire match and corresponding $MBEGIN, $MEND:  useful in
   parameter substitutions like ${.../.../...}.
 - (#s) and (#e) match start and end of pattern like ^ and $ in regular
   expression, useful in complex expressions such as ((#s)|/)dirname((#e)|/)
   and in parameter expressions.

 - Depth-first/last listing of recursive glob lists

Functions etc.:
 - `autoload -X' inside a function body instructs the shell to
   bootstrap the function at that point
 - `autoload +X fn' says load the function fn but don't execute it
 - Prompt `themes' make customization of prompts easier

Modules:
 - New hierarchical naming scheme for modules; supplied modules go into
   zsh subdirectory, so zle becomes zsh/zle etc.; aliases supplied for
   compatibility for existing code, but the new format should be used in
   future.
 - zmodload is more consistent between dynamically and statically linked
   shells
 - zsh/zftp and its function suite support multiple sessions (zfsession
   command); zftransfer allows transfer of files between two ftp sessions
   with no local file; use styles for e.g. progress style; IPv6 supported;
   recursive put `zfput -r' for uploads
 - zsh/zpty module creates pseudoterminal and allows builtin `expect'-like
   behaviour

Other:
 - Test suite, not yet complete (`make test')
 - use of Linux task limits
 - Many fixes including output redirection with `setopt xtrace' and
   other redirection fixes; NIS+ problem.
 - Better null-command behaviour in sh and csh emulation
 - Internal memory usage optimisations


New features in zsh version 3.1.6 (beta version)
------------------------------------------------
Note also the changes for 3.0.6, which include changes between 3.1.5. and
3.1.6.

New completion system via shell functions; massive degree of
programmability and configurability:
 - ready-made function suite to use, see zshcompsys(1)
 - approximate completion and spelling correction via completion
 - control over matching for case-independence, partial word completion, etc.
 - menu selection:  choose a completion by moving the cursor
 - coloured completion lists
 - completion of filenames in quotes is now more reliable; splitting
   quoted strings into command arguments is also possible.

Other editing changes:
  - enhancements to function/editing interface:  new parameters, numeric
    arguments, string argument passing, reading keys from widgets.
  - the old history-search-{back,for}ward behaviour and bindings have
    returned (up to minor details).
  - BASH_AUTO_LIST option to show completion list only on second key press.
  - the ZBEEP parameter gives a string to output instead of beeping,
    allowing you to have a visual bell.

History changes: new options HIST_NO_FUNCTIONS, HIST_EXPIRE_DUPS_FIRST,
HIST_FIND_NO_DUPS, HIST_IGNORE_ALL_DUPS, INC_APPEND_HISTORY,
HIST_SAVE_NO_DUPS, SHARE_HISTORY, allow better control of when history is
read and written and how duplicates are handled.  New format for history
saves.

Associative arrays plus enhanced parameter substitutions to retrieve keys
and values.

Globbing changes:
  - Case-insensitive and approximate globbing.
  - Ordering and indexing of globbing matches, e.g. *(om[1]) picks
    most recently modified file.
  - General file mode qualifier with chmod(1)-like syntax, e.g. *(f:u+wx:)

New loadable modules:
  - zftp, plus associated function suite, for turning your zsh session
    into an FTP session too
  - parameter, for examining and altering shell hash tables via an
    associative array interface.
  - mapfile, for reading and writing external files via an associative
    array interface.

Debugging and prompt enhancements:
  - $PS4 can contain %i for $LINENO as well as %N for script or function
    names (default PS4 changed), also %_ for current shell structure
    executing;
  - Prompt truncation %<...< is now more flexible: it applies to a
    whole section of the prompt, not just one escape.  You need to put
    %<< after the truncated escape to get the old behaviour.
  - %20(l.yes.no) in prompts prints yes if at least 20 characters have
    been output, else no (e.g. for outputting extra newlines).

Parameter and expansion changes
  - `typeset -t MYPATH mypath' creates tied path/PATH-like variables
  - `typeset -g' allows operations on parameters without making them local
  - New expansions
    - ${(t)param} prints type information for $param
    - ${(P)param} treats value of $param as the name of a param to
      substitute
    - ${foo:q} can quote replaced parameter text from expansion
    - ${foo/old/new} substitution, like bash; also (S) flag for shortest
      match
    - $foo[(b.2.i)bar] starts searching $foo for bar starting at 2nd match

Builtin and function changes
  - stat module: `stat -H hash foo' gives you e.g. $hash[mtime]
  - `autoload -U' autoloads functions without alias expansion.

Other new options:
  - LOCAL_TRAPS allows signal traps to be local to functions (as in ksh).
  - NO_RCS can now be turned on at any point in initialization files.
  - NO_GLOBAL_RCS can force /etc/z* files after /etc/zshenv to be skipped.
    (Please don't use this as an excuse to stuff more into /etc/zshenv!)
  - Existing MAGIC_EQUAL_SUBST option is more useful; any argument containing
    ...=~...:~... will perform filename expansion on the ~ (previously,
    the string before `=' had to look like a parameter name).

Configuration changes:
  - Generation of signal names should be more reliable
  - Customizable installation of shell functions from distribution.


New features in zsh version 3.0.6
---------------------------------

Most of these changes are designed to improve compatibility with zsh
version 3.1.6, the latest development release.  However, this release also
fixes all known Year 2000 (Y2K) bugs in zsh 3.0.

History changes:
  - whitespace between words is ignored in history searches.
  - new option HIST_REDUCE_BLANKS removes extra whitespace in the stored
    history.
  - support for reading (but not writing) version 3.1.6 history files.

Globbing changes:
  - the a, c, and m glob qualifiers can now test time in seconds.
  - globbing of number ranges behaves more like character ranges in that
    it can match a prefix of a number, e.g. `<1-5>*' matches 1, 2, 3, 4,
    5, 17, 23skiddoo, 5986, etc., but not 6, 7, 8ball, 911, etc.

Parameter and expansion changes:
  - expansion of ~ and other globbing flags via ${~param} do not depend
    upon EXTENDED_GLOB (bug fix).
  - nested parameter substitutions require braces (this was always the
    documented behaviour, but previous parsers didn't enforce it).
  - quote only nested expansion, e.g. ${(f)"$(<file)"} reads complete
    `file', then splits lines into array.

Builtin and function changes:
  - `typeset -U' works on the colon-array version of linked parameters.
  - `typeset +f' and `functions +' output the names (only) of functions.
  - `emulate -L' has the effect of `setopt localoptions'.
  - in fn1() { local foo; unset foo; foo=bar; }, foo is restored at local
    level, whereas if the `unset foo' appeared in a nested function it
    would have been restored at global level, which was presumably wrong.
  - `foo=bar >&file' is a redirection, not a NULLCMD.
  - any single complex command, such as `case ... esac', parses as if
    semicolon-terminated (bug fix).
  - the shell function `preexec', if defined, is run after parsing each
    command line but before executing the command.

Other changes:
  - the option PRINT_EIGHT_BIT causes zsh to emit raw bytes in prompts
    and completion lists even if the system ctype(3) package says that
    those bytes are not "printable."

Debugging enhancements:
  - LINENO is now very much more useful in scripts and functions and is
    reported correctly in most error messages.
  - ERREXIT behaviour is now consistent with newer Bourne-like shells,
    e.g. with respect to `if' tests that fail.

Configuration changes:
  - Large file and 64-bit integers on 32-bit machines supported where
    provided by OS.
  - a few more system features, such as getpwnam/getpwuid, are tested for.


New features in zsh version 3.1 (beta version)
----------------------------------------------

On most operating systems zsh can load binary modules dynamically at
run-time.  ZLE and the compctl builtin are now reside in a separate
module which is loaded automatically on demand.

for ((expr; expr; expr)) do ... done loop syntax from AT&T ksh93 is
now supported.

POSIX globbing character classes ([:alnum:] etc.) are now supported.

ksh's case fall-through feature (;&) is supported.

ksh93's $'' quoting syntax is supported.

Restricted mode is now supported.  This is controlled by the new option
RESTRICTED (-r).

New options BARE_GLOB_QUAL, HIST_NO_FUNCTIONS (alias NO_LOG), KSH_GLOB,
PRINT_EIGHT_BIT, PROMPT_BANG, PROMPT_PERCENT, RM_STAR_WAIT.

Options ALWAYS_LAST_PROMPT, APPEND_HISTORY, AUTO_LIST, AUTO_MENU,
AUTO_PARAM_KEYS, AUTO_PARAM_SLASH, AUTO_REMOVE_SLASH, LIST_AMBIGUOUS
and LIST_TYPES are now on by default.

In ZLE, arbitrarily many keymaps can be defined.  Multi-character
keybindings now work.

Completion can be performed within a brace expansion.

EMACS-like universal-argument function.


New features in zsh version 3.0
-------------------------------

Trailing "/" in a glob pattern now works like in other shell thus it
can no longer be used as a shorthand for "(/)".

Much improved sh/ksh emulation.  When zsh is invoked as sh it mostly
conforms to POSIX 1003.2.

Enhanced parameter expansion features: new flags: A, @, e, W, p, f, F.
Expansions can be nested.  For example,
"${${(M)${(f@)$(<builtin.pro)}:#char*}[2][(w)3]}" expands to the third
word of the second line of builtin.pro which begins with char.  See
zshexpn(1) for the details.

***/foo glob does recursive directory search following symbolic links.

Traps defined by the trap builtin are now executed in the current shell
environment and not as a shell function.  This means that $1 is not set
to the signal number.  Of course the TRAPxxx functions continue working
as before.

Traps defined by the trap builtin are reset to their default values in
subshells.

Option names can be prefixed by `no' to unset an option.
setopt no_option_name is the same as unsetopt option_name.
This change affects the output of the setopt and unsetopt
builtins when these are invoked without arguments.  See
the zshoptions manual page for more explanation.

!, {, } and [[ are now reserved words.  Things like [[-z $foo]] or {foo}
should not be used.  {foo} still works if the IGNORE_BRACES option is not
set but this feature may be removed in the future.  [[ -z $foo ]] and
{ foo } should be used instead.

HOSTTYPE special parameter is removed.  The new OSTYPE, MACHTYPE and
VENDOR parameters should be used instead.

VERSION parameter is renamed to ZSH_VERSION

exec now saves the history in interactive shells.  If you do not like this
behaviour you can alias exec to 'unset HISTFILE ; exec'.

${~spec}, ${=spec} and ${^spec} used to toggle the effect of
globsubst/shwordsplit/rcexpandparam.  Now these force the corresponding
option on. ~, = or ^ can be doubled to force the relevant option off for
the substitution.

Explicitly requested word splitting like ${=spec} or ${(s:delim:)spec}
will be executed even if the substitution is double quoted.

The right-hand side of assignments are no longer globbed by default hence
assignment foo=* will assign '*' as a value of foo.  Use the foo=( * )
array assignment syntax to get the old behaviour.  Alternatively the
GLOB_ASSIGN can be set to emulate the old behaviour but the usage of this
option is strongly discouraged and this option may be completely removed in
the future.

foo=$bar no longer creates an array even if bar is an array.  Use
foo=( $bar ) or even better, foo=( "$bar[@]" ) instead.

When foo is an array parameter ${#foo} will always return the length of the
array even if the substitution is double quoted.  ${(c)#foo} should be used
to get back the old behaviour.

When the prompt_subst option is set prompts are fully expanded using
parameter expansion, command substitution and arithmetic expansion.
In 2.5 backquote substitution was not performed in the prompts so this
change might cause problems in some startup scripts if ` is used literally
in prompts.

History substitution is now not performed if the history escape character
appears in a single-quoted string.  This may break some interactive shell
functions which use \! in single-quoted strings.

The UID, EUID, GID, EGID parameters can be assigned now. The assignment
executes the setuid(), seteuid(), setgid(), setegid() respectively.  On
systems where setuid and seteuid is not supported these functions are
emulated using setreuid or setresuid which may result in a different
behaviour.

Assigning the USERNAME parameter will call setuid(uid) where uid is the
user id of the specified user.

The privileged (-p) option is automatically set on invocation if euid != uid
or egid != gid.  If this option is set no user startup files are sourced.
The shell will drop privileges when this option is unset by resetting its
euid to uid and its egid to gid.

The =number substitution for accessing the directory stack is changed to
~number to allow =command substitution when a command name begins with a
digit.

<> is a redirection operator which opens the standard input for both
reading and writing.  To match a number use <->.

Option letters -1 and -C for PRINT_EXIT_VALUE and NO_CLOBBER are swapped:
`set -C' sets NO_CLOBBER and `set -1' sets PRINT_EXIT_VALUE.

AUTO_PUSHD behaviour is changed.  Now cd without arguments will always go
to the $HOME directory even if AUTO_PUSHD is set and PUSHD_TO_HOME is not
set.  If you preferred the old behaviour you can alias cd to pushd.

IFS word splitting with SH_WORD_SPLIT and the splitting of the input in the
read builtin has changed in cases when IFS contains characters other than
<space>, <tab>, <newline>.  See the description of IFS in the zshparam
manual page for more details.


New features in zsh version 2.5
-------------------------------

Greatly expanded completion possibilities.  Programmable completion
allows detailed control over what arguments of what commands can be
completed to what.  See dots/zcomp in the distribution for examples.

Expand filenames with ~ and = on the right hand side of parameter
assignments.  New option MAGIC_EQUAL_SUBST to do it in all
identifier=expression arguments.

${+name} becomes 1 or 0 if name is set or unset.  ${~spec} toggles
GLOB_SUBST in substitution.  Parameter substitution takes lots
of flags in the format ${(flags)name}.

New glob qualifiers for block/character special files, times in glob
qualifiers can be in months, weeks, days, hours, minutes.  Qualifiers can
work on links or on what they point to.  Qualifiers separated by commas
are or-ed.

New parameter substitution modifiers (fFwW) to repeat actions.  New
option CSH_JUNKIE_HISTORY.

New line editor functions history-beginning-search-backward,
history-beginning-search-forward, expand-or-complete-prefix, push-input,
push-line-or-edit.

Assign to part of a string, use qualifiers on string subscription with
$foo[(qual)2,5]

New parameters: EGID, EUID, KEYTIMEOUT

New prompt escape sequence %_ to get constructs like for and while in
the secondary prompt.  %E in prompt clears to end of screen.

Conditional expressions in PROMPT and WATCHFMT.

New options ALWAYS_LAST_PROMPT, ALWAYS_TO_END, AUTO_PARAM_KEYS,
COMPLETE_ALIASES, COMPLETE_IN_WORD, CSH_JUNKIE_HISTORY, GLOB_SUBST,
LIST_AMBIGUOUS, MAGIC_EQUAL_SUBST, NO_FLOW_CONTROL, PROMPT_SUBST

New option -m to many builtins makes arguments subject to pattern
matching.

Bindkey can now bind both key sequences and prefixes of those.  You can
for example bind ESC and function keys sending ESC sequences.

Additional options to read builtin to use in functions called by
completion.

New options to print to sort arguments and print them in columns.

Some additional resource limits can be specified.

Some editor functions now work in the minibuffer.
