defcustom for ^L display?

[Drew Adams]

For possible consideration after the release - Let users customize how they
want ^L to appear in buffers.

Here is one approach, to give an idea:

(defcustom ^L-appearance-vector
  (vconcat (make-vector 10 ?_) " Section (Printable Page) "
           (make-vector 10 ?_))
  "Vector determining how a Control-l character is displayed.
Either a vector of characters or nil.  The characters are displayed in
place of the Control-l character.  nil means `^L' is displayed.

Some possible values (evaluate the Lisp expressions first):
 nil: ^L
 (make-vector 50 ?_): Horizontal line
 (vconcat (make-vector 10 ?_)
         \" Section (Printable Page) \" (make-vector 10 ?_)): WYSIWYG"

  :initialize 'custom-initialize-changed'
  :set (lambda (symb val)
         (set-default symb val)
         (aset standard-display-table ?\014 ^L-appearance-vector))
  :type '(choice
          (const :tag "^L" nil)
          (restricted-sexp :match-alternatives (vectorp)
           :tag "Vector of characters to display"))
  :group 'convenience :group 'wp)

(aset standard-display-table ?\014 ^L-appearance-vector)

Some people might prefer nil as the default value, but if newbies are the
target for the uncustomized value, then a default value something like that
shown here might be better.