Each Emacs Lisp package should have one main customization group which contains all the options, faces and other groups in the package. If the package has a small number of options and faces, use just one group and put everything in it. When there are more than twenty or so options and faces, then you should structure them into subgroups, and put the subgroups under the package’s main customization group. It is OK to put some of the options and faces in the package’s main group alongside the subgroups.
The package’s main or only group should be a member of one or more of
the standard customization groups. (To display the full list of them,
use M-x customize.) Choose one or more of them (but not too
many), and add your group to each of them using the :group
keyword.
The way to declare new customization groups is with defgroup.
Declare group as a customization group containing members. Do not quote the symbol group. The argument doc specifies the documentation string for the group.
The argument members is a list specifying an initial set of
customization items to be members of the group. However, most often
members is nil, and you specify the group’s members by
using the :group keyword when defining those members.
If you want to specify group members through members, each element
should have the form (name widget). Here name
is a symbol, and widget is a widget type for editing that symbol.
Useful widgets are custom-variable for a variable,
custom-face for a face, and custom-group for a group.
When you introduce a new group into Emacs, use the :version
keyword in the defgroup; then you need not use it for
the individual members of the group.
In addition to the common keywords (see Common Item Keywords), you can
also use this keyword in defgroup:
:prefix prefix ¶If the name of an item in the group starts with prefix, and the
customizable variable custom-unlispify-remove-prefixes is
non-nil, the item’s tag will omit prefix. A group can
have any number of prefixes.
The variables, faces, and subgroups of a group are stored in the
custom-group property of the group’s symbol. See Accessing Symbol Properties. The value of that property is a list of pairs whose
car is the symbol of the variable or the face or the subgroup,
and the cdr is one of the corresponding symbols
custom-variable, custom-face, or custom-group.
If this variable is non-nil, the prefixes specified by a
group’s :prefix keyword are omitted from tag names, whenever
the user customizes the group.
The default value is nil, i.e., the prefix-discarding feature
is disabled. This is because discarding prefixes often leads to
confusing names for options and faces.