For customization purposes, settings are organized into groups
to help you find them. Groups are collected into bigger groups, all
the way up to a master group called Emacs.
M-x customize creates a customization buffer that shows the
top-level Emacs group and the second-level groups immediately
under it. It looks like this, in part:
/- Emacs group: Customization of the One True Editor. -------------\
[State]: visible group members are all at standard values.
See also [Manual].
[Editing] : Basic text editing facilities.
[External] : Interfacing to external utilities.
more second-level groups
\- Emacs group end ------------------------------------------------/
This says that the buffer displays the contents of the Emacs
group. The other groups are listed because they are its contents. But
they are listed differently, without indentation and dashes, because
their contents are not included. Each group has a single-line
documentation string; the Emacs group also has a ‘[State]’
line.
Most of the text in the customization buffer is read-only, but it typically includes some editable fields that you can edit. There are also buttons and links, which do something when you invoke them. To invoke a button or a link, either click on it with Mouse-1, or move point to it and type <RET>.
For example, the phrase ‘[State]’ that appears in a second-level group is a button. It operates on the same customization buffer. Each group name, such as ‘[Editing]’, is a hypertext link to that group; invoking it creates a new customization buffer, showing the group and its contents.
The Emacs group only contains other groups. These groups, in
turn, can contain settings or still more groups. By browsing the
hierarchy of groups, you will eventually find the feature you are
interested in customizing. Then you can use the customization buffer
to set that feature's settings. You can also go straight to a
particular group by name, using the command M-x customize-group.