What does ^L in (Emacs Lisp) source code mean?

Question

Several times I see ^L in (mostly Emacs Lisp) source codes that looks like are separators of larger logical groups. Is it their real purpose? And if so, how can I use them? Is there a built-in Emacs functionality that utilize it?

None of the answers have mentioned that `^L` is just the default value. You can set a buffer-local `page-delimiter` regexp to anything you want, to get page navigation functionality using some custom value. — phils, Aug 20 '17 at 09:52
This is the [form feed character](https://en.wikipedia.org/wiki/Page_break#Form_feed), often represented as `\x0c` or `\f` — Boris Verkhovskiy, Feb 13 '21 at 23:35

score 39 · Answer 1 · edited Oct 16 '09 at 11:09

39

The Emacs commands backward-page and forward-page (C-x [ and C-x ]), among others, take advantage of ^Ls placed in the code as separators.

The habit did not propagate much to languages other than Emacs-lisp, but most languages treat ^L as a blank, so you can use these separators in your favorite language if you like the idea. You can type your own ^Ls with C-q C-l.

edited Oct 16 '09 at 11:09

viam0Zah

25,949
8
77
100

answered Oct 16 '09 at 09:02

Pascal Cuoq

79,187
7
161
281

score 29 · Accepted Answer · edited Aug 19 '17 at 15:33

29

This is a page break.

[...]

A page break can also be used for a logical separation of source-code sections. Emacs has commands and key bindings that use page breaks, such as ‘forward-page’ (C-x ] or C-]), ‘backward-page’ (C-x [ or C-[), and 'narrow-to-page' (C-x n p). Other functions, such as ‘mark-page’, operate on the content of a page. See also PageMode.

edited Aug 19 '17 at 15:33

Yuri Tretyakov

11
2

answered Oct 16 '09 at 08:43

7

Otherwise known as a FORM-FEED character to people who remember line printers. – pavium Oct 16 '09 at 08:47
1

Btw, they are in RFCs too (in .txts), but firefox doesn't show them. – andre-r Oct 16 '09 at 09:27

score 6 · Answer 3 · edited Nov 30 '09 at 08:31

6

When exploring a big file with multiple of such "pages" the function "narrow-to-page" (C-x n p) is handy: it hides everything not in the current page. Then for example searching for a function name to see the callers only leads to matches in that section, so you can really focus on understanding the narrowed region.

Use widen (C-x n w) to see the whole file again.

edited Nov 30 '09 at 08:31

viam0Zah

25,949
8
77
100

answered Nov 28 '09 at 12:38

zut

806
4
12

score 5 · Answer 4 · answered Sep 04 '11 at 00:29

5

See also Pretty Control-L if you want to change how Control-l characters appear -- e.g., use a highlighted line instead of just ^L.

answered Sep 04 '11 at 00:29

Drew

29,895
7
74
104

score 2 · Answer 5 · answered Oct 16 '09 at 08:56

That is indeed a page break character, which on older line printers skipped to the next page or paper. Code-wise, it does nothing; it is only there to split the code into larger sections. There are convenient Emacs commands to jump to the next and previous "page", and inserting these characters takes advantage of that.

What does ^L in (Emacs Lisp) source code mean?

5 Answers5