(input-mode-8-bit): Fix the customization.

lisp/simple.el

@@ -3501,17 +3501,20 @@ or go back to just one window (by deleting all but the selected window)."
 
 (define-key global-map "\e\e\e" 'keyboard-escape-quit)
 
-(defcustom input-mode-8-bit nil
-  "Toggle whether 8-bit keyboard input is accepted.
+(defcustom input-mode-8-bit t
+  "Control acceptance of 8-bit keyboard input.
 This may be useful for inputting non-ASCII characters if your keyboard
-can generate them.
+can generate them.  It is not necessary to change this under a window
+system which can distinguish 8-bit characters and Meta keys.
 Setting this variable directly does not take effect;
 use either M-x customize or the function `set-input-mode'."
   :set (lambda (symbol value)
 	 (let ((mode (current-input-mode)))
 	   (set-input-mode (nth 0 mode) (nth 1 mode) value)))
   :initialize 'custom-initialize-default
-  :type 'boolean
+  :type '(choice (const :tag "8-bit input for a Meta key" t)
+		 (const :tag "Direct 8-bit character input" 0)
+		 (const :tag "Assume top bit is parity and ignore" nil))
   :version "21.1"
   :link '(custom-manual "Single-Byte European Support")
   :group 'keyboard)