This page is about Control-l (`##^L##') characters in text.

== ^L Is a Section Separator and a Printable-Page Separator ==

Many people embed a `##^L##' in text to separate it into sections. In Emacs, these sections are called ''pages'', and you can navigate among them using commands with `page' in their name: `backward-page', `forward-page', and so on. You can also search for the character `##^L##' by using `C-s C-q C-l'. There are additional Emacs commands for manipulating pages, including `mark-page', `narrow-to-page', and `count-lines-page'.

The `##^L##' character is also known as the ''form-feed'' character. In many printers, including the old line printers, it causes the printer to advance a page, hence its use as a "page" separator in Emacs. Be aware of this, especially if `##^L##' is used in a file more as a section separator, where the section length is sometimes quite short. Before printing such a file, you might want to strip the `##^L##' characters or replace them by newline characters; otherwise, you will print lots of relatively empty pages.

== Controlling the Appearance of ^L in Text== 

By default, depending on your value of option `ctl-arrow', a `##^L##' in text appears as `##^L##' or as `##\014##' (the octal code for the character). You can change this appearance by changing the character's value in the current display table -- see the Emacs-Lisp manual, section Display Tables http://www.gnu.org/software/emacs/elisp-manual/html_mono/elisp.html#Display-Tables), for more information about this.

Here is one way to do this. This code is from Lisp:oneonone.el.

  (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)

This code just defines a customizable variable, `##^L-appearance-vector##', whose value is either a vector of characters to display in place of `##^L##', or `nil' for the default appearance of  `##^L##'.

The suggested value ##(make-vector 50 ?_)## shows a string of 50 underscore characters, in other words, a horizontal line. That's just the appearance; the underscore characters are not part of your text.

The suggested value ##(vconcat (make-vector 10 ?_) \" Section (Printable Page) \" (make-vector 10 ?_))## shows this:

<nowiki>__________ Section (Printable Page) __________</nowiki>

You must use the code ##(aset standard-display-table ?\014 ^L-appearance-vector)## once, to let Emacs know to use the variable. After that, whenever you customize the variable, the appearance is changed immediately.

You can get creative, changing the appearance to suit your context. You can also bind such a variable to different values (so, different appearances) in different Emacs contexts. For example, a major-mode might use a buffer-local value of this to show `##^L##' in a special way that is appropriate to that mode. Or, you can adapt the code to use a different display table from the `standard-display-table', one that is specific to your mode.

The same idea of changing the display-table value can of course be used to change the appearance of any character, not just `##^L##'. 

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CategoryDisplay
CategoryDotEmacs
CategoryCustomize
OneOnOneEmacs