Commit ac742142 authored by Stefan Monnier's avatar Stefan Monnier

* etc/NEWS.1-17: Use outline-mode and a more standard format

parent 857c2c27
......@@ -8,21 +8,21 @@ This file is about changes in emacs versions 1 through 17.
Changes in Emacs 17
* Changes in Emacs 17
* Frustrated?
** Frustrated?
Try M-x doctor.
* Bored?
** Bored?
Try M-x hanoi.
* Brain-damaged?
** Brain-damaged?
Try M-x yow.
* Sun3, Tahoe, Apollo, HP9000s300, Celerity, NCR Tower 32,
** Sun3, Tahoe, Apollo, HP9000s300, Celerity, NCR Tower 32,
Sequent, Stride, Encore, Plexus and AT&T 7300 machines supported.
The Tahoe, Sun3, Sequent and Celerity use 4.2. In regard to the
......@@ -30,24 +30,24 @@ Apollo, see the file APOLLO in this directory. NCR Tower32,
HP9000s300, Stride and Nu run forms of System V. System V rel 2 also
works on Vaxes now. See etc/MACHINES.
* System V Unix supported, including subprocesses.
** System V Unix supported, including subprocesses.
It should be possible now to bring up Emacs on a machine running
mere unameliorated system V Unix with no major work; just possible bug
fixes. But you can expect to find a handful of those on any machine
that Emacs has not been run on before.
* Berkeley 4.1 Unix supported.
** Berkeley 4.1 Unix supported.
See etc/MACHINES.
* Portable `alloca' provided.
** Portable `alloca' provided.
Emacs can now run on machines that do not and cannot support the library
subroutine `alloca' in the canonical fashion, using an `alloca' emulation
written in C.
* On-line manual.
** On-line manual.
Info now contains an Emacs manual, with essentially the same text
as in the printed manual.
......@@ -57,7 +57,7 @@ The manual can now be printed with a standard TeX.
Nicely typeset and printed copies of the manual are available
from the Free Software Foundation.
* Backup file version numbers.
** Backup file version numbers.
Emacs now supports version numbers in backup files.
......@@ -108,7 +108,7 @@ to keep, overriding `dired-kept-versions'. A negative argument specifies
the number of oldest versions to keep, using minus the argument to override
`kept-old-versions'.
* Immediate conflict detection.
** Immediate conflict detection.
Emacs now locks the files it is modifying, so that if
you start to modify within Emacs a file that is being
......@@ -130,27 +130,27 @@ directory. If such a directory is not provided and told to
Emacs as part of configuring it for your machine, the lock feature
is turned off.
* M-x recover-file.
** M-x recover-file.
This command is used to get a file back from an auto-save
(after a system crash, for example). It takes a file name
as argument and visits that file, but gets the data from the
file's last auto save rather than from the file itself.
* M-x normal-mode.
** M-x normal-mode.
This command resets the current buffer's major mode and local
variables to be as specified by the visit filename, the -*- line
and/or the Local Variables: block at the end of the buffer.
It is the same thing normally done when a file is first visited.
* Echo area messages disappear shortly if minibuffer is in use.
** Echo area messages disappear shortly if minibuffer is in use.
Any message in the echo area disappears after 2 seconds
if the minibuffer is active. This allows the minibuffer
to become visible again.
* C-z on System V runs a subshell.
** C-z on System V runs a subshell.
On systems which do not allow programs to be suspended, the C-z command
forks a subshell that talks directly to the terminal, and then waits
......@@ -158,18 +158,18 @@ for the subshell to exit. This gets almost the effect of suspending
in that you can run other programs and then return to Emacs. However,
you cannot log out from the subshell.
* C-c is always a prefix character.
** C-c is always a prefix character.
Also, subcommands of C-c which are letters are always
reserved for the user. No standard Emacs major mode
defines any of them.
* Picture mode C-c commands changed.
** Picture mode C-c commands changed.
The old C-c k command is now C-c C-w.
The old C-c y command is now C-c C-x.
* Shell mode commands changed.
** Shell mode commands changed.
All the special commands of Shell mode are now moved onto
the C-c prefix. Most are not changed aside from that.
......@@ -182,7 +182,7 @@ is now C-c C-o, and C-x C-v (show output) is now C-c C-r.
The old M-= (copy previous input) command is now C-c C-y.
* Shell mode recognizes aliases for `pushd', `popd' and `cd'.
** Shell mode recognizes aliases for `pushd', `popd' and `cd'.
Shell mode now uses the variable `shell-pushd-regexp' as a
regular expression to recognize any command name that is
......@@ -194,13 +194,13 @@ There are also `shell-popd-regexp' to recognize commands
with the effect of a `popd', and `shell-cd-regexp' to recognize
commands with the effect of a `cd'.
* "Exit" command in certain modes now C-c C-c.
** "Exit" command in certain modes now C-c C-c.
These include electric buffer menu mode, electric command history
mode, Info node edit mode, and Rmail edit mode. In all these
modes, the command to exit used to be just C-c.
* Outline mode changes.
** Outline mode changes.
Lines that are not heading lines are now called "body" lines.
The command `hide-text' is renamed to `hide-body'.
......@@ -212,7 +212,7 @@ Changes of line visibility are no longer undoable. As a result,
they no longer use up undo memory and no longer interfere with
undoing earlier commands.
* Rmail changes.
** Rmail changes.
The s and q commands now both expunge deleted messages before saving;
use C-x C-s to save without expunging.
......@@ -229,23 +229,23 @@ o now outputs to an Rmail file, and C-o to a Unix mail file.
The F command (rmail-find) is renamed to M-s (rmail-search).
Various new commands and features exist; see the Emacs manual.
* Local bindings described first in describe-bindings.
** Local bindings described first in describe-bindings.
* [...], {...} now balance in Fundamental mode.
** [...], {...} now balance in Fundamental mode.
* Nroff mode and TeX mode.
** Nroff mode and TeX mode.
There are two new major modes for editing nroff input and TeX input.
See the Emacs manual for full information.
* New C indentation style variable `c-brace-imaginary-offset'.
** New C indentation style variable `c-brace-imaginary-offset'.
The value of `c-brace-imaginary-offset', normally zero, controls the
indentation of a statement inside a brace-group where the open-brace
is not the first thing on a line. The value says where the open-brace
is imagined to be, relative to the first nonblank character on the line.
* Dired improvements.
** Dired improvements.
Dired now normally keeps the cursor at the beginning of the file name,
not at the beginning of the line. The most used motion commands are
......@@ -259,22 +259,22 @@ printed in an error message.
If the `v' command is invoked on a file which is a directory,
dired is run on that directory.
* `visit-tag-table' renamed `visit-tags-table'.
** `visit-tag-table' renamed `visit-tags-table'.
This is so apropos of `tags' finds everything you need to
know about in connection with Tags.
* `mh-e' library uses C-c as prefix.
** `mh-e' library uses C-c as prefix.
All the special commands of `mh-rmail' now are placed on a
C-c prefix rather than on the C-x prefix. This is for
consistency with other special modes with their own commands.
* M-$ or `spell-word' checks word before point.
** M-$ or `spell-word' checks word before point.
It used to check the word after point.
* Quitting during autoloading no longer causes trouble.
** Quitting during autoloading no longer causes trouble.
Now, when a file is autoloaded, all function redefinitions
and `provide' calls are recorded and are undone if you quit
......@@ -284,14 +284,14 @@ As a result, it no longer happens that some of the entry points
which are normally autoloading have been defined already, but the
entire file is not really present to support them.
* `else' can now be indented correctly in C mode.
** `else' can now be indented correctly in C mode.
TAB in C mode now knows which `if' statement an `else' matches
up with, and can indent the `else' correctly under the `if',
even if the `if' contained such things as another `if' statement,
or a `while' or `for' statement, with no braces around it.
* `batch-byte-compile'
** `batch-byte-compile'
Runs byte-compile-file on the files specified on the command line.
All the rest of the command line arguments are taken as files to
......@@ -300,7 +300,7 @@ Must be used only with -batch, and kills emacs on completion.
Each file will be processed even if an error occurred previously.
For example, invoke `emacs -batch -f batch-byte-compile *.el'.
* `-batch' changes.
** `-batch' changes.
`-batch' now implies `-q': no init file is loaded by Emacs when
`-batch' is used. Also, no `term/TERMTYPE.el' file is loaded. Auto
......@@ -313,7 +313,7 @@ One echo-area message that is not suppressed is the one that says
that a file is being loaded. That is because you can prevent this
message by passing `t' as the third argument to `load'.
* Display of search string in incremental search.
** Display of search string in incremental search.
Now, when you type C-s or C-r to reuse the previous search
string, that search string is displayed immediately in the echo area.
......@@ -321,23 +321,23 @@ string, that search string is displayed immediately in the echo area.
Three dots are displayed after the search string while search
is actually going on.
* View commands.
** View commands.
The commands C-x ], C-x [, C-x /, C-x j and C-x o are now
available inside `view-buffer' and `view-file', with their
normal meanings.
* Full-width windows preferred.
** Full-width windows preferred.
The ``other-window'' commands prefer other full width windows,
and will split only full width windows.
* M-x rename-file can copy if necessary.
** M-x rename-file can copy if necessary.
When used between different file systems, since actual renaming does
not work, the old file will be copied and deleted.
* Within C-x ESC, you can pick the command to repeat.
** Within C-x ESC, you can pick the command to repeat.
While editing a previous command to be repeated, inside C-x ESC,
you can now use the commands M-p and M-n to pick an earlier or
......@@ -353,24 +353,24 @@ The command you finally execute using C-x ESC is added to the
front of the command history, unless it is identical with the
first thing in the command history.
* Use C-c C-c to exit from editing within Info.
** Use C-c C-c to exit from editing within Info.
It used to be C-z for this. Somehow this use of C-z was
left out when all the others were moved. The intention is that
C-z should always suspend Emacs.
* Default arg to C-x < and C-x > now window width minus 2.
** Default arg to C-x < and C-x > now window width minus 2.
These commands, which scroll the current window horizontally
by a specified number of columns, now scroll a considerable
distance rather than a single column if used with no argument.
* Auto Save Files Deleted.
** Auto Save Files Deleted.
The default value of `delete-auto-save-files' is now `t', so that
when you save a file for real, its auto save file is deleted.
* Rnews changes.
** Rnews changes.
The N, P and J keys in Rnews are renamed to M-n, M-p and M-j.
These keys move among newsgroups.
......@@ -382,7 +382,7 @@ this change, are eliminated.
The s command for outputting the current article to a file
is renamed as o, to be compatible with Rmail.
* Sendmail changes.
** Sendmail changes.
If you have a ~/.mailrc file, Emacs searches it for mailing address
aliases, and these aliases are expanded when you send mail in Emacs.
......@@ -407,15 +407,15 @@ The new variable `mail-header-separator' now specifies the string
to use on the line that goes between the headers and the message text.
By default it is still "--text follows this line--".
* Command history truncated automatically.
** Command history truncated automatically.
Just before each garbage collection, all but the last 30 elements
of the command history are discarded.
Incompatible Lisp Programming Changes in Emacs 17
* Incompatible Lisp Programming Changes in Emacs 17
* `&quote' no longer supported.
** `&quote' no longer supported.
This feature, which allowed Lisp functions to take arguments
that were not evaluated, has been eliminated, because it is
......@@ -434,7 +434,7 @@ with
(defun foo-1 (x y z) ...
* Functions `region-to-string' and `region-around-match' removed.
** Functions `region-to-string' and `region-around-match' removed.
These functions were made for compatibility with Gosling Emacs, but it
turns out to be undesirable to use them in GNU Emacs because they use
......@@ -450,24 +450,24 @@ the two functions `match-beginning' and `match-end'. These give
you one bound at a time, as a numeric value, without changing
point or the mark.
* Function `function-type' removed.
** Function `function-type' removed.
This just appeared not to be very useful. It can easily be written in
Lisp if you happen to want it. Just use `symbol-function' to get the
function definition of a symbol, and look at its data type or its car
if it is a list.
* Variable `buffer-number' removed.
** Variable `buffer-number' removed.
You can still use the function `buffer-number' to find out
a buffer's unique number (assigned in order of creation).
* Variable `executing-macro' renamed `executing-kbd-macro'.
** Variable `executing-macro' renamed `executing-kbd-macro'.
This variable is the currently executing keyboard macro, as
a string, or `nil' when no keyboard macro is being executed.
* Loading term/$TERM.
** Loading term/$TERM.
The library term/$TERM (where $TERM get replaced by your terminal
type), which is done by Emacs automatically when it starts up, now
......@@ -478,12 +478,12 @@ term-$TERM; thus, for example, term-vt100.el, but now they live
in a special subdirectory named term, and have names like
term/vt100.el.
* `command-history' format changed.
** `command-history' format changed.
The elements of this list are now Lisp expressions which can
be evaluated directly to repeat a command.
* Unused editing commands removed.
** Unused editing commands removed.
The functions `forward-to-word', `backward-to-word',
`upcase-char', `mark-beginning-of-buffer' and `mark-end-of-buffer'
......@@ -491,9 +491,9 @@ have been removed. Their definitions can be found in file
lisp/unused.el if you need them.
Upward Compatible Lisp Programming Changes in Emacs 17
* Upward Compatible Lisp Programming Changes in Emacs 17
* You can now continue after errors and quits.
** You can now continue after errors and quits.
When the debugger is entered because of a C-g, due to
a non-`nil' value of `debug-on-quit', the `c' command in the debugger
......@@ -513,7 +513,7 @@ is not valid, another error occurs.
Errors signaled with the function `error' cannot be continued.
If you try to continue, the error just happens again.
* `dot' renamed `point'.
** `dot' renamed `point'.
The word `dot' has been replaced with `point' in all
function and variable names, including:
......@@ -526,7 +526,7 @@ function and variable names, including:
The old names are still supported, for now.
* `string-match' records position of end of match.
** `string-match' records position of end of match.
After a successful call to `string-match', `(match-end 0)' will
return the index in the string of the first character after the match.
......@@ -534,7 +534,7 @@ Also, `match-begin' and `match-end' with nonzero arguments can be
used to find the indices of beginnings and ends of substrings matched
by subpatterns surrounded by parentheses.
* New function `insert-before-markers'.
** New function `insert-before-markers'.
This function is just like `insert' except in the handling of any
relocatable markers that are located at the point of insertion.
......@@ -542,7 +542,7 @@ With `insert', such markers end up pointing before the inserted text.
With `insert-before-markers', they end up pointing after the inserted
text.
* New function `copy-alist'.
** New function `copy-alist'.
This function takes one argument, a list, and makes a disjoint copy
of the alist structure. The list itself is copied, and each element
......@@ -552,30 +552,30 @@ remain shared with the original argument.
This is what it takes to get two alists disjoint enough that changes
in one do not change the result of `assq' on the other.
* New function `copy-keymap'.
** New function `copy-keymap'.
This function takes a keymap as argument and returns a new keymap
containing initially the same bindings. Rebindings in either one of
them will not alter the bindings in the other.
* New function `copy-syntax-table'.
** New function `copy-syntax-table'.
This function takes a syntax table as argument and returns a new
syntax table containing initially the same syntax settings. Changes
in either one of them will not alter the other.
* Randomizing the random numbers.
** Randomizing the random numbers.
`(random t)' causes the random number generator's seed to be set
based on the current time and Emacs's process id.
* Third argument to `modify-syntax-entry'.
** Third argument to `modify-syntax-entry'.
The optional third argument to `modify-syntax-entry', if specified
should be a syntax table. The modification is made in that syntax table
rather than in the current syntax table.
* New function `run-hooks'.
** New function `run-hooks'.
This function takes any number of symbols as arguments.
It processes the symbols in order. For each symbol which
......@@ -584,7 +584,7 @@ called as a function, with no arguments.
This is useful in major mode commands.
* Second arg to `switch-to-buffer'.
** Second arg to `switch-to-buffer'.
If this function is given a non-`nil' second argument, then the
selection being done is not recorded on the selection history.
......@@ -592,7 +592,7 @@ The buffer's position in the history remains unchanged. This
feature is used by the view commands, so that the selection history
after exiting from viewing is the same as it was before.
* Second arg to `display-buffer' and `pop-to-buffer'.
** Second arg to `display-buffer' and `pop-to-buffer'.
These two functions both accept an optional second argument which
defaults to `nil'. If the argument is not `nil', it means that
......@@ -602,7 +602,7 @@ the selected window.
This feature is used by `switch-to-buffer-other-window'.
* New variable `completion-ignore-case'.
** New variable `completion-ignore-case'.
If this variable is non-`nil', completion allows strings
in different cases to be considered matching. The global value
......@@ -614,13 +614,13 @@ to change the value globally, but you might not like the consequences
in the many situations (buffer names, command names, file names)
where case makes a difference.
* Major modes related to Text mode call text-mode-hook, then their own hooks.
** Major modes related to Text mode call text-mode-hook, then their own hooks.
For example, turning on Outline mode first calls the value of
`text-mode-hook' as a function, if it exists and is non-`nil',
and then does likewise for the variable `outline-mode-hook'.
* Defining new command line switches.
** Defining new command line switches.
You can define a new command line switch in your .emacs file
by putting elements on the value of `command-switch-alist'.
......@@ -638,26 +638,26 @@ examine this variable, and do
(setq command-line-args (cdr command-line-args)
to "use up" an argument.
* New variable `load-in-progress'.
** New variable `load-in-progress'.
This variable is non-`nil' when a file of Lisp code is being read
and executed by `load'.
* New variable `print-length'.
** New variable `print-length'.
The value of this variable is normally `nil'. It may instead be
a number; in that case, when a list is printed by `prin1' or
`princ' only that many initial elements are printed; the rest are
replaced by `...'.
* New variable `find-file-not-found-hook'.
** New variable `find-file-not-found-hook'.
If `find-file' or any of its variants is used on a nonexistent file,
the value of `find-file-not-found-hook' is called (if it is not `nil')
with no arguments, after creating an empty buffer. The file's name
can be found as the value of `buffer-file-name'.
* Processes without buffers.
** Processes without buffers.
In the function `start-process', you can now specify `nil' as
the process's buffer. You can also set a process's buffer to `nil'
......@@ -672,7 +672,7 @@ When a process has no buffer, its output is lost unless it has a
filter, and no indication of its being stopped or killed is given
unless it has a sentinel.
* New function `user-variable-p'. `v' arg prompting changed.
** New function `user-variable-p'. `v' arg prompting changed.
This function takes a symbol as argument and returns `t' if
the symbol is defined as a user option variable. This means
......@@ -686,7 +686,7 @@ user variables.
The function `read-variable' also now accepts and completes
over user variables only.
* CBREAK mode input is the default in Unix 4.3 bsd.
** CBREAK mode input is the default in Unix 4.3 bsd.
In Berkeley 4.3 Unix, there are sufficient features for Emacs to
work fully correctly using CBREAK mode and not using SIGIO.
......@@ -695,7 +695,7 @@ This mode corresponds to `nil' as the first argument to
`set-input-mode'. You can still select either mode by calling
that function.
* Information on memory usage.
** Information on memory usage.
The new variable `data-bytes-used' contains the number
of bytes of impure space allocated in Emacs.
......@@ -704,18 +704,18 @@ Emacs could allocate. Note that space formerly allocated
and freed again still counts as `used', since it is still
in Emacs's address space.
* No limit on size of output from `format'.
** No limit on size of output from `format'.
The string output from `format' used to be truncated to
100 characters in length. Now it can have any length.
* New errors `void-variable' and `void-function' replace `void-symbol'.
** New errors `void-variable' and `void-function' replace `void-symbol'.
This change makes it possible to have error messages that
clearly distinguish undefined variables from undefined functions.
It also allows `condition-case' to handle one case without the other.
* `replace-match' handling of `\'.
** `replace-match' handling of `\'.
In `replace-match', when the replacement is not literal,
`\' in the replacement string is always treated as an
......@@ -728,19 +728,19 @@ This level of escaping is comparable with what goes on in
a regular expression. It is over and above the level of `\'
escaping that goes on when strings are read in Lisp syntax.
* New error `invalid-regexp'.
** New error `invalid-regexp'.
A regexp search signals this type of error if the argument does
not meet the rules for regexp syntax.
* `kill-emacs' with argument.
** `kill-emacs' with argument.
If the argument is a number, it is returned as the exit status code
of the Emacs process. If the argument is a string, its contents
are stuffed as pending terminal input, to be read by another program
after Emacs is dead.
* New fifth argument to `subst-char-in-region'.
** New fifth argument to `subst-char-in-region'.
This argument is optional and defaults to `nil'. If it is not `nil',
then the substitutions made by this function are not recorded
......@@ -749,7 +749,7 @@ in the Undo mechanism.
This feature should be used with great care. It is now used
by Outline mode to make lines visible or invisible.
* ` *Backtrace*' buffer renamed to `*Backtrace*'.
** ` *Backtrace*' buffer renamed to `*Backtrace*'.
As a result, you can now reselect this buffer easily if you switch to
another while in the debugger.
......@@ -757,7 +757,7 @@ another while in the debugger.
Exiting from the debugger kills the `*Backtrace*' buffer, so you will
not try to give commands in it when no longer really in the debugger.
* New function `switch-to-buffer-other-window'.
** New function `switch-to-buffer-other-window'.
This is the new primitive to select a specified buffer (the
argument) in another window. It is not quite the same as
......@@ -768,7 +768,7 @@ leave the current window's old buffer displayed as well.
All functions to select a buffer in another window should
do so by calling this new function.
* New variable `minibuffer-help-form'.
** New variable `minibuffer-help-form'.
At entry to the minibuffer, the variable `help-form' is bound
to the value of `minibuffer-help-form'.
......@@ -779,7 +779,7 @@ the definition of C-h as a command). `minibuffer-help-form'
can be used to provide a different default way of handling
C-h while in the minibuffer.
* New \{...} documentation construct.
** New \{...} documentation construct.
It is now possible to set up the documentation string for
a major mode in such a way that it always describes the contents
......@@ -799,23 +799,23 @@ For example, the documentation string for the function `c-mode' contains
Variables controlling indentation style:
...
* New character syntax class "punctuation".
** New character syntax class "punctuation".
Punctuation characters behave like whitespace in word and
list parsing, but can be distinguished in regexps and in the
function `char-syntax'. Punctuation syntax is represented by
a period in `modify-syntax-entry'.
* `auto-mode-alist' no longer needs entries for backup-file names,
** `auto-mode-alist' no longer needs entries for backup-file names,
Backup suffixes of all kinds are now stripped from a file's name
before searching `auto-mode-alist'.
Changes in Emacs 16
* Changes in Emacs 16
* No special code for Ambassadors, VT-100's and Concept-100's.
** No special code for Ambassadors, VT-100's and Concept-100's.
Emacs now controls these terminals based on the termcap entry, like
all other terminals. Formerly it did not refer to the termcap entries
......@@ -827,24 +827,24 @@ fixing up the termcap entry. See ./TERMS for more info.
See ./TERMS in any case if you find that some terminal does not work
right with Emacs now.
* Minibuffer default completion character is TAB (and not ESC).
** Minibuffer default completion character is TAB (and not ESC).
So that ESC can be used in minibuffer for more useful prefix commands.
* C-z suspends Emacs in all modes.
** C-z suspends Emacs in all modes.
Formerly, C-z was redefined for other purposes by certain modes,
such as Buffer Menu mode. Now other keys are used for those purposes,
to keep the meaning of C-z uniform.
* C-x ESC (repeat-complex-command) allows editing the command it repeats.
** C-x ESC (repeat-complex-command) allows editing the command it repeats.
Instead of asking for confirmation to re-execute a command from the
command history, the command is placed, in its Lisp form, into the
minibuffer for editing. You can confirm by typing RETURN, change some
arguments and then confirm, or abort with C-g.
* Incremental search does less redisplay on slow terminals.
** Incremental search does less redisplay on slow terminals.
If the terminal baud rate is <= the value of `isearch-slow-speed',
incremental searching outside the text on the screen creates
......@@ -857,7 +857,7 @@ The initial value of `isearch-slow-speed' is 1200.
This feature is courtesy of crl@purdue.
* Recursive minibuffers not allowed.
** Recursive minibuffers not allowed.
If the minibuffer window is selected, most commands that would
use the minibuffer gets an error instead. (Specific commands
......@@ -873,7 +873,7 @@ you can probably understand recursive minibuffers.
This may be overridden by binding the variable
`enable-recursive-minibuffers' to t.
* New major mode Emacs-Lisp mode, for editing Lisp code to run in Emacs.
** New major mode Emacs-Lisp mode, for editing Lisp code to run in Emacs.
The mode in which emacs lisp files is edited is now called emacs-lisp-mode
and is distinct from lisp-mode. The latter is intended for use with
......@@ -884,7 +884,7 @@ called emacs-lisp-mode-hook. A consequence of this changes is that
.emacs init files which set the value of lisp-mode-hook may need to be
changed to use the new names.
* Correct matching of parentheses is checked on insertion.