+;; The identity of a customize option is represented by a Lisp symbol.
+;; The following values are associated with an option.
+
+;; 0. The current value.
+
+;; This is the value of the option as seen by "the rest of Emacs".
+
+;; Usually extracted by 'default-value', but can be extracted with
+;; different means if the option symbol has the 'custom-get'
+;; property. Similarly, set-default (or the 'custom-set' property)
+;; can set it.
+
+;; 1. The widget value.
+
+;; This is the value shown in the widget in a customize buffer.
+
+;; 2. The customized value.
+
+;; This is the last value given to the option through customize.
+
+;; It is stored in the 'customized-value' property of the option, in a
+;; cons-cell whose car evaluates to the customized value.
+
+;; 3. The saved value.
+
+;; This is last value saved from customize.
+
+;; It is stored in the 'saved-value' property of the option, in a
+;; cons-cell whose car evaluates to the saved value.
+
+;; 4. The standard value.
+
+;; This is the value given in the 'defcustom' declaration.
+
+;; It is stored in the 'standard-value' property of the option, in a
+;; cons-cell whose car evaluates to the standard value.
+
+;; 5. The "think" value.
+
+;; This is what customize thinks the current value should be.
+
+;; This is the customized value, if any such value exists, otherwise
+;; the saved value, if that exists, and as a last resort the standard
+;; value.
+
+;; The reason for storing values unevaluated: This is so you can have
+;; values that depend on the environment. For example, you can have a
+;; variable that has one value when Emacs is running under a window
+;; system, and another value on a tty. Since the evaluation is only done
+;; when the variable is first initialized, this is only relevant for the
+;; saved (and standard) values, but affect others values for
+;; compatibility.
+
+;; You can see (and modify and save) this unevaluated value by selecting
+;; "Show initial Lisp expression" from the Lisp interface. This will
+;; give you the unevaluated saved value, if any, otherwise the
+;; unevaluated standard value.
+
+;; The possible states for a customize widget are:
+
+;; 0. unknown
+
+;; The state has not been determined yet.
+
+;; 1. modified
+
+;; The widget value is different from the current value.
+
+;; 2. changed
+
+;; The current value is different from the "think" value.
+
+;; 3. set
+
+;; The "think" value is the customized value.
+
+;; 4. saved
+
+;; The "think" value is the saved value.
+
+;; 5. standard
+
+;; The "think" value is the standard value.
+
+;; 6. rogue
+
+;; There is no standard value. This means that the variable was
+;; not defined with defcustom, nor handled in cus-start.el. You
+;; can not create a Custom buffer for such variables using the
+;; normal interactive Custom commands. However, such Custom
+;; buffers can be created in other ways, for instance, by calling
+;; `customize-option' non-interactively.
+
+;; 7. hidden
+
+;; There is no widget value.
+
+;; 8. mismatch
+
+;; The widget value is not valid member of the :type specified for the
+;; option.
+