9.4.2 Standard Symbol Properties

Here, we list the symbol properties which are used for special purposes in Emacs. In the following table, whenever we say “the named function”, that means the function whose name is the relevant symbol; similarly for “the named variable” etc.

:advertised-binding

This property value specifies the preferred key binding, when showing documentation, for the named function. See Substituting Key Bindings in Documentation.

char-table-extra-slots

The value, if non-nil, specifies the number of extra slots in the named char-table type. See Char-Tables.

customized-face

face-defface-spec

saved-face

theme-face

These properties are used to record a face’s standard, saved, customized, and themed face specs. Do not set them directly; they are managed by defface and related functions. See Defining Faces.

customized-value

saved-value

standard-value

theme-value

These properties are used to record a customizable variable’s standard value, saved value, customized-but-unsaved value, and themed values. Do not set them directly; they are managed by defcustom and related functions. See Defining Customization Variables.

definition-name

This property is used to find the definition of a symbol in the source code, when it might be hard to find the definition by textual search of the source file. For example, a define-derived-mode (see Defining Derived Modes) might define a mode-specific function or a variable implicitly; or your Lisp program might generate a run-time call to defun to define a function (see Defining Functions). In these and similar cases, the definition-name property of the symbol should be another symbol whose definition can be found by textual search and whose code defines the original symbol. In the example with define-derived-mode, the value of this property of the functions and variables it defines should be the mode symbol. The Emacs Help commands such as C-h f (see Help in The GNU Emacs Manual) use this property to show the definition of a symbol via a button in the *Help* buffer where the symbol’s documentation is shown.

disabled

If the value is non-nil, the named function is disabled as a command. See Disabling Commands.

face-documentation

The value stores the documentation string of the named face. This is set automatically by defface. See Defining Faces.

history-length

The value, if non-nil, specifies the maximum minibuffer history length for the named history list variable. See Minibuffer History.

interactive-form

The value is an interactive form for the named function. Normally, you should not set this directly; use the interactive special form instead. See Interactive Call.

menu-enable

The value is an expression for determining whether the named menu item should be enabled in menus. See Simple Menu Items.

mode-class

If the value is special, the named major mode is special. See Major Mode Conventions.

permanent-local

If the value is non-nil, the named variable is a buffer-local variable whose value should not be reset when changing major modes. See Creating and Deleting Buffer-Local Bindings.

permanent-local-hook

If the value is non-nil, the named function should not be deleted from the local value of a hook variable when changing major modes. See Setting Hooks.

pure ¶

If the value is non-nil, the named function is considered to be pure (see What Is a Function?). Calls with constant arguments can be evaluated at compile time. This may shift run time errors to compile time. Not to be confused with pure storage (see Pure Storage).

risky-local-variable

If the value is non-nil, the named variable is considered risky as a file-local variable. See File Local Variables.

safe-function

If the value is non-nil, the named function is considered generally safe for evaluation. See Determining whether a Function is Safe to Call.

safe-local-eval-function

If the value is non-nil, the named function is safe to call in file-local evaluation forms. See File Local Variables.

safe-local-variable

The value specifies a function for determining safe file-local values for the named variable. See File Local Variables. Since this value is consulted when loading files, the function should be efficient and should ideally not lead to loading any libraries to determine the safeness (e.g., it should not be an autoloaded function).

side-effect-free ¶

A non-nil value indicates that the named function is free of side effects (see What Is a Function?), so the byte compiler may ignore a call whose value is unused. If the property’s value is error-free, the byte compiler may even delete such unused calls. In addition to byte compiler optimizations, this property is also used for determining function safety (see Determining whether a Function is Safe to Call).

important-return-value ¶

A non-nil value makes the byte compiler warn about code that calls the named function without using its returned value. This is useful for functions where doing so is likely to be a mistake.

undo-inhibit-region

If non-nil, the named function prevents the undo operation from being restricted to the active region, if undo is invoked immediately after the function. See Undo.

variable-documentation

If non-nil, this specifies the named variable’s documentation string. This is set automatically by defvar and related functions. See Defining Faces.