custom-group-menu is a variable defined in `cus-edit.el'.
Its value is shown below.

Alist of actions for the `custom-group' widget.
Each entry has the form (NAME ACTION FILTER) where NAME is the name of
the menu entry, ACTION is the function to call on the widget when the
menu is selected, and FILTER is a predicate which takes a `custom-group'
widget as an argument, and returns non-nil if ACTION is valid on that
widget. If FILTER is nil, ACTION is always valid.


(("Set for Current Session" custom-group-set (lambda (widget) (eq (widget-get widget :custom-state) 'modified))) ("Undo Edits" custom-group-reset-current (lambda (widget) (memq (widget-get widget :custom-state) '(modified)))) ("Revert This Session's Customizations" custom-group-reset-saved (lambda (widget) (memq (widget-get widget :custom-state) '(modified set)))))