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(emacs)Changing an Option
Changing an Option
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Here is an example of what a user option looks like in the
customization buffer:
Kill Ring Max: [Hide] 60
[State]: this option is unchanged from its standard setting.
Maximum length of kill ring before oldest elements are thrown away.
The text following `[Hide]', `60' in this case, indicates the
current value of the option. If you see `[Show]' instead of `[Hide]',
it means that the value is hidden; the customization buffer initially
hides values that take up several lines. Invoke `[Show]' to show the
value.
The line after the option name indicates the "customization state"
of the option: in the example above, it says you have not changed the
option yet. The word `[State]' at the beginning of this line is
active; you can get a menu of various operations by invoking it with
`Mouse-1' or <RET>. These operations are essential for customizing the
variable.
The line after the `[State]' line displays the beginning of the
option's documentation string. If there are more lines of
documentation, this line ends with `[More]'; invoke this to show the
full documentation string.
To enter a new value for `Kill Ring Max', move point to the value
and edit it textually. For example, you can type `M-d', then insert
another number.
When you begin to alter the text, you will see the `[State]' line
change to say that you have edited the value:
[State]: you have edited the value as text, but not set the option.
Editing the value does not actually set the option variable. To do
that, you must "set" the option. To do this, invoke the word `[State]'
and choose `Set for Current Session'.
The state of the option changes visibly when you set it:
[State]: you have set this option, but not saved it for future sessions.
You don't have to worry about specifying a value that is not valid;
setting the option checks for validity and will not really install an
unacceptable value.
While editing a value or field that is a file name, directory name,
command name, or anything else for which completion is defined, you can
type `M-<TAB>' (`widget-complete') to do completion.
Some options have a small fixed set of possible legitimate values.
These options don't let you edit the value textually. Instead, an
active field `[Value Menu]' appears before the value; invoke this field
to edit the value. For a boolean "on or off" value, the active field
says `[Toggle]', and it changes to the other value. `[Value Menu]' and
`[Toggle]' edit the buffer; the changes take effect when you use the
`Set for Current Session' operation.
Some options have values with complex structure. For example, the
value of `file-coding-system-alist' is an association list. Here is
how it appears in the customization buffer:
File Coding System Alist: [Hide]
[INS] [DEL] File regexp: \.elc\'
Choice: [Value Menu] Encoding/decoding pair:
Decoding: emacs-mule
Encoding: emacs-mule
[INS] [DEL] File regexp: \(\`\|/\)loaddefs.el\'
Choice: [Value Menu] Encoding/decoding pair:
Decoding: raw-text
Encoding: raw-text-unix
[INS] [DEL] File regexp: \.tar\'
Choice: [Value Menu] Encoding/decoding pair:
Decoding: no-conversion
Encoding: no-conversion
[INS] [DEL] File regexp:
Choice: [Value Menu] Encoding/decoding pair:
Decoding: undecided
Encoding: nil
[INS]
[State]: this option is unchanged from its standard setting.
Alist to decide a coding system to use for a file I/O operation. [Hide]
The format is ((PATTERN . VAL) ...),
where PATTERN is a regular expression matching a file name,
[...more lines of documentation...]
Each association in the list appears on four lines, with several
editable or "active" fields. You can edit the regexps and coding
systems using ordinary editing commands. You can also invoke `[Value
Menu]' to switch to a kind of value--for instance, to specify a
function instead of a pair of coding systems.
To delete an association from the list, invoke the `[DEL]' button
for that item. To add an association, invoke `[INS]' at the position
where you want to add it. There is an `[INS]' button between each pair
of association, another at the beginning and another at the end, so you
can add the new association at any position in the list.
Two special commands, <TAB> and `S-<TAB>', are useful for moving
through the customization buffer. <TAB> (`widget-forward') moves
forward to the next active or editable field; `S-<TAB>'
(`widget-backward') moves backward to the previous active or editable
field.
Typing <RET> on an editable field also moves forward, just like
<TAB>. We set it up this way because people often type <RET> when they
are finished editing a field. To insert a newline within an editable
field, use `C-o' or `C-q C-j'.
Setting the option changes its value in the current Emacs session;
"saving" the value changes it for future sessions as well. This works
by writing code into your `~/.emacs' file so as to set the option
variable again each time you start Emacs. To save the option, invoke
`[State]' and select the `Save for Future Sessions' operation.
If Emacs was invoked with the `-q' or `--no-init-file' options
(Note: Initial Options), it will not let you save your customizations
in your `~/.emacs' init file. This is because saving customizations
from such a session would wipe out all the other customizations you
might have on your init file.
You can also restore the option to its standard value by invoking
`[State]' and selecting the `Erase Customization' operation. There are
actually three reset operations:
`Reset'
If you have made some modifications and not yet set the option,
this restores the text in the customization buffer to match the
actual value.
`Reset to Saved'
This restores the value of the option to the last saved value, and
updates the text accordingly.
`Erase Customization'
This sets the option to its standard value, and updates the text
accordingly. This also eliminates any saved value for the option,
so that you will get the standard value in future Emacs sessions.
Sometimes it is useful to record a comment about a specific
customization. Use the `Add Comment' item from the `[State]' menu to
create a field for entering the comment. The comment you enter will be
saved, and displayed again if you again view the same option in a
customization buffer, even in another session.
The state of a group indicates whether anything in that group has
been edited, set or saved. You can select `Set for Current Session',
`Save for Future Sessions' and the various kinds of `Reset' operation
for the group; these operations on the group apply to all options in
the group and its subgroups.
Near the top of the customization buffer there are two lines
containing several active fields:
[Set for Current Session] [Save for Future Sessions]
[Reset] [Reset to Saved] [Erase Customization] [Finish]
Invoking `[Finish]' either buries or kills this customization buffer
according to the setting of the option `custom-buffer-done-function';
the default is to bury the buffer. Each of the other fields performs
an operation--set, save or reset--on each of the items in the buffer
that could meaningfully be set, saved or reset.
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