The `^L' appeared in built-in help.

The `^L' appeared in built-in help.

[Hongyi Zhao]

I noticed so many `^L' appeared in Emacs' built-in help. According to
the ascii document shown below, this should mean '\f' (form feed):

$ man ascii | grep ' L$'
       014   12    0C    FF  '\f' (form feed)        114   76    4C    L

But I also noticed that this control character is not used evenly
throughout the document.

Any hints for this phenomenon?

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

RE: [External] : The `^L' appeared in built-in help.

[Drew Adams]

> Any hints for this phenomenon?

A form-feed char (Control L) has from the outset
been used as an ASCII control character, to cause
a new page to be advance (fed) on old printers.

Emacs leverages this old meaning by using it as
a page separator, for <whatever> meaning of "page".
Emacs has page-movement commands that make use of
this character, just as it has line-oriented
commands that make use of line ending chars such
as newline.

Try `C-x ]'.

See the Emacs manual, node Pages:

https://www.gnu.org/software/emacs/manual/html_node/emacs/Pages.html

`C-h r' is your friend, along with his buddy, `i'.
`C-h r i page TAB', then choose a completion such
as `pages' or `page-delimiter'.

Re: [External] : The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Drew Adams wrote:

>> Any hints for this phenomenon?
>
> A form-feed char (Control L) has from the outset been used
> as an ASCII control character, to cause a new page to be
> advance (fed) on old printers.

But they are also transformed into buttons, a pretty exotic
interactive feature, in `gnus-article-mode' buffers :)

\f

innit?

-- 
underground experts united
https://dataswamp.org/~incal

RE: [External] : The `^L' appeared in built-in help.

[Drew Adams]

[-- Attachment #1: Type: text/plain, Size: 559 bytes --]

> >> Any hints for this phenomenon?
> >
> > A form-feed char (Control L) has from the outset been used
> > as an ASCII control character, to cause a new page to be
> > advance (fed) on old printers.
> 
> But they are also transformed into buttons, a pretty exotic
> interactive feature, in `gnus-article-mode' buffers :)
> innit?

You can also customize how you want ^L chars displayed,
to appear as better page separators.  See Pretty Control L:

https://emacswiki.org/emacs/PrettyControlL

https://www.emacswiki.org/emacs/download/pp-c-l.el

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Re: [External] : The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Drew Adams wrote:

>>>> Any hints for this phenomenon?
>>>
>>> A form-feed char (Control L) has from the outset been used
>>> as an ASCII control character, to cause a new page to be
>>> advance (fed) on old printers.
>> 
>> But they are also transformed into buttons, a pretty exotic
>> interactive feature, in `gnus-article-mode' buffers
>> :) innit?
>
> You can also customize how you want ^L chars displayed, to
> appear as better page separators. See Pretty Control L:
>
> https://emacswiki.org/emacs/PrettyControlL
>
> https://www.emacswiki.org/emacs/download/pp-c-l.el

...

Why is there such big interest in this?

-- 
underground experts united
https://dataswamp.org/~incal

RE: [External] : The `^L' appeared in built-in help.

[Drew Adams]

[-- Attachment #1: Type: text/plain, Size: 65 bytes --]

> Why is there such big interest in this?

Who said there is?

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Re: [External] : The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Drew Adams wrote:

>> Why is there such big interest in this?
>
> Who said there is?

I don't remember, didn't you say that?

Several people are talking about it and it was recently up as
well here (I actually have an more distant memory of it coming
up here as well, so I've seen this question 3 times) and now
there are hyperlinks to tutorials how to configure it?
And a bug report?

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> I noticed so many `^L' appeared in Emacs' built-in help.
> According to the ascii document shown below, this should
> mean '\f' (form feed):
>
> $ man ascii | grep ' L$'
>        014   12    0C    FF  '\f' (form feed)        114   76    4C    L
>
> But I also noticed that this control character is not used
> evenly throughout the document.
>
> Any hints for this phenomenon?

This was discussed here not long ago! See if you can grep the
archives! [1]

They are used to delimit

\f

pages!

M-x insert-char RET FORM FEED (FF) RET

[1] http://lists.gnu.org/archive/html/help-gnu-emacs/

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Tue, Jul 6, 2021 at 10:55 AM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Hongyi Zhao wrote:
>
> > I noticed so many `^L' appeared in Emacs' built-in help.
> > According to the ascii document shown below, this should
> > mean '\f' (form feed):
> >
> > $ man ascii | grep ' L$'
> >        014   12    0C    FF  '\f' (form feed)        114   76    4C    L
> >
> > But I also noticed that this control character is not used
> > evenly throughout the document.
> >
> > Any hints for this phenomenon?
>
> This was discussed here not long ago! See if you can grep the
> archives! [1]
>
> They are used to delimit
>
>
>
> pages!
>
> M-x insert-char RET FORM FEED (FF) RET
>

But `M-x describe-char RET' for `^L' in scratch buffer shows the following:

            to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"

And the above-mentioned two type input sequences will generated
different characters:

"C-x 8 RET c" --->  `^F'
"C-x 8 RET FORM FEED (FF)" --->  `^L'

> [1] http://lists.gnu.org/archive/html/help-gnu-emacs/

Are there some built-in Emacs commands for searching this mail archive
conveniently?

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> But `M-x describe-char RET' for `^L' in scratch buffer shows
> the following:
>
> to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"
>
> And the above-mentioned two type input sequences will
> generated different characters:
>
> "C-x 8 RET c" --->  `^F'
> "C-x 8 RET FORM FEED (FF)" --->  `^L'

I get ^L for both

\f

of

\f

them

> Are there some built-in Emacs commands for searching this
> mail archive conveniently?

Yes, Gnus and Gmane, the mailing list help-gnu-emacs is then,
as an NNTP group, called gmane.emacs.help.

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

[-- Attachment #1: Type: text/plain, Size: 1022 bytes --]

On Tue, Jul 6, 2021 at 12:07 PM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Hongyi Zhao wrote:
>
> > But `M-x describe-char RET' for `^L' in scratch buffer shows
> > the following:
> >
> > to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"
> >
> > And the above-mentioned two type input sequences will
> > generated different characters:
> >
> > "C-x 8 RET c" --->  `^F'
> > "C-x 8 RET FORM FEED (FF)" --->  `^L'
>
> I get ^L for both
>
> of
>
> them

Strange. See the screenshot in attachment.

>
> > Are there some built-in Emacs commands for searching this
> > mail archive conveniently?
>
> Yes, Gnus and Gmane, the mailing list help-gnu-emacs is then,
> as an NNTP group, called gmane.emacs.help.
>
> --
> underground experts united
> https://dataswamp.org/~incal
>
>


-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

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Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

[-- Attachment #1: Type: text/plain, Size: 1435 bytes --]

On Tue, Jul 6, 2021 at 4:26 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
>
> On Tue, Jul 6, 2021 at 12:07 PM Emanuel Berg via Users list for the
> GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
> >
> > Hongyi Zhao wrote:
> >
> > > But `M-x describe-char RET' for `^L' in scratch buffer shows
> > > the following:
> > >
> > > to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"
> > >
> > > And the above-mentioned two type input sequences will
> > > generated different characters:
> > >
> > > "C-x 8 RET c" --->  `^F'
> > > "C-x 8 RET FORM FEED (FF)" --->  `^L'
> >
> > I get ^L for both
> >
> > of
> >
> > them
>
> Strange. See the screenshot in attachment.

And see the `M-x describe-char RET' for it in the attachment.

>
> >
> > > Are there some built-in Emacs commands for searching this
> > > mail archive conveniently?
> >
> > Yes, Gnus and Gmane, the mailing list help-gnu-emacs is then,
> > as an NNTP group, called gmane.emacs.help.
> >
> > --
> > underground experts united
> > https://dataswamp.org/~incal
> >
> >
>
>
> --
> Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
> Theory and Simulation of Materials
> Hebei Vocational University of Technology and Engineering
> NO. 552 North Gangtie Road, Xingtai, China



-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

[-- Attachment #2: 2021-07-06_16-29.png --]
[-- Type: image/png, Size: 188011 bytes --]

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

>>>> "C-x 8 RET c" --->  `^F'
>>>> "C-x 8 RET FORM FEED (FF)" --->  `^L'
>>>
>>> I get ^L for both
>>>
>>> of
>>>
>>> them
>>
>> Strange. See the screenshot in attachment.
>
> And see the `M-x describe-char RET' for it in the attachment.

?

It says you input it with `C-x 8 RET 6', which is correct?
You get it with `C-x 8 RET c', for real? In that case I don't
know?

Increase the face size? :P That's a "c" as in "cipher"...

>> Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
>> Theory and Simulation of Materials
>> Hebei Vocational University of Technology and Engineering
>> NO. 552 North Gangtie Road, Xingtai, China

Cool job! But no 996 I hope! However
RFC 3676, section 4.3 (Usenet Signature Convention)
https://www.ietf.org/rfc/rfc3676.txt

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Tue, Jul 6, 2021 at 5:13 PM Emanuel Berg via Users list for the GNU
Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Hongyi Zhao wrote:
>
> >>>> "C-x 8 RET c" --->  `^F'
> >>>> "C-x 8 RET FORM FEED (FF)" --->  `^L'
> >>>
> >>> I get ^L for both
> >>>
> >>> of
> >>>
> >>> them
> >>
> >> Strange. See the screenshot in attachment.
> >
> > And see the `M-x describe-char RET' for it in the attachment.
>
> ?
>
> It says you input it with `C-x 8 RET 6', which is correct?
> You get it with `C-x 8 RET c', for real? In that case I don't
> know?
>

The screenshot is generated by `C-x 8 RET c', but `M-x describe-char
RET' for the result character says that it should be input by `C-x 8
RET 6', as you can see in the screenshot. So, I'm confused on this
problem.

> Increase the face size? :P That's a "c" as in "cipher"...
>

I still can't understand what is your meaning.

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> The screenshot is generated by `C-x 8 RET c', but `M-x
> describe-char RET' for the result character says that it
> should be input by `C-x 8 RET 6', as you can see in the
> screenshot. So, I'm confused on this problem.

Here are mine, C-x 8 RET 6 RET



and C-x 8 RET c RET

\f

and M-x insert-char RET form feed (ff) RET

\f

The char that looks like ^F is:

             position: 894 of 959 (93%), restriction: <544-960>, column: 0
            character: C-f (displayed as C-f) (codepoint 6, #o6, #x6)
              charset: ascii (ASCII (ISO646 IRV))
code point in charset: 0x06
               script: latin
               syntax: . 	which means: punctuation
             to input: type "C-x 8 RET 6" or "C-x 8 RET ACKNOWLEDGE"
          buffer code: #x06
            file code: #x06 (encoded by coding system utf-8-emacs)
              display: terminal code #x06
       hardcoded face: escape-glyph

Character code properties: customize what to show
  old-name: ACKNOWLEDGE
  general-category: Cc (Other, Control)

There are text properties here:
  fontified            t

and the char that looks like ^L is:

             position: 950 of 1750 (54%), restriction: <544-1751>, column: 0
            character: C-l (displayed as C-l) (codepoint 12, #o14, #xc)
              charset: ascii (ASCII (ISO646 IRV))
code point in charset: 0x0C
               script: latin
               syntax:   	which means: whitespace
             to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"
          buffer code: #x0C
            file code: #x0C (encoded by coding system utf-8-emacs)
              display: terminal code #x0C
       hardcoded face: escape-glyph

Character code properties: customize what to show
  old-name: FORM FEED (FF)
  general-category: Cc (Other, Control)

There are text properties here:
  fontified            t

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Tue, Jul 6, 2021 at 6:46 PM Emanuel Berg via Users list for the GNU
Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Hongyi Zhao wrote:
>
> > The screenshot is generated by `C-x 8 RET c', but `M-x
> > describe-char RET' for the result character says that it
> > should be input by `C-x 8 RET 6', as you can see in the
> > screenshot. So, I'm confused on this problem.
>
> Here are mine, C-x 8 RET 6 RET
>
>
>
> and C-x 8 RET c RET
>
>
>
> and M-x insert-char RET form feed (ff) RET
>
>
>
> The char that looks like ^F is:
>
>              position: 894 of 959 (93%), restriction: <544-960>, column: 0
>             character: C-f (displayed as C-f) (codepoint 6, #o6, #x6)
>               charset: ascii (ASCII (ISO646 IRV))
> code point in charset: 0x06
>                script: latin
>                syntax: .        which means: punctuation
>              to input: type "C-x 8 RET 6" or "C-x 8 RET ACKNOWLEDGE"
>           buffer code: #x06
>             file code: #x06 (encoded by coding system utf-8-emacs)
>               display: terminal code #x06
>        hardcoded face: escape-glyph
>
> Character code properties: customize what to show
>   old-name: ACKNOWLEDGE
>   general-category: Cc (Other, Control)
>
> There are text properties here:
>   fontified            t
>
> and the char that looks like ^L is:
>
>              position: 950 of 1750 (54%), restriction: <544-1751>, column: 0
>             character: C-l (displayed as C-l) (codepoint 12, #o14, #xc)
>               charset: ascii (ASCII (ISO646 IRV))
> code point in charset: 0x0C
>                script: latin
>                syntax:          which means: whitespace
>              to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"
>           buffer code: #x0C
>             file code: #x0C (encoded by coding system utf-8-emacs)
>               display: terminal code #x0C
>        hardcoded face: escape-glyph
>
> Character code properties: customize what to show
>   old-name: FORM FEED (FF)
>   general-category: Cc (Other, Control)
>
> There are text properties here:
>   fontified            t
>

I find the clues: if I run `emacs -Q', the results will be the same as
yours. If I run  `emacs', the problem reported here will happen. So
the problem is triggered by some configurations in my
`~/.emacs.d/init.el'. But I still can't find out the specific
configuration which caused the problem.

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Tue, Jul 6, 2021 at 7:07 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
>
> On Tue, Jul 6, 2021 at 6:46 PM Emanuel Berg via Users list for the GNU
> Emacs text editor <help-gnu-emacs@gnu.org> wrote:
> >
> > Hongyi Zhao wrote:
> >
> > > The screenshot is generated by `C-x 8 RET c', but `M-x
> > > describe-char RET' for the result character says that it
> > > should be input by `C-x 8 RET 6', as you can see in the
> > > screenshot. So, I'm confused on this problem.
> >
> > Here are mine, C-x 8 RET 6 RET
> >
> >
> >
> > and C-x 8 RET c RET
> >
> >
> >
> > and M-x insert-char RET form feed (ff) RET
> >
> >
> >
> > The char that looks like ^F is:
> >
> >              position: 894 of 959 (93%), restriction: <544-960>, column: 0
> >             character: C-f (displayed as C-f) (codepoint 6, #o6, #x6)
> >               charset: ascii (ASCII (ISO646 IRV))
> > code point in charset: 0x06
> >                script: latin
> >                syntax: .        which means: punctuation
> >              to input: type "C-x 8 RET 6" or "C-x 8 RET ACKNOWLEDGE"
> >           buffer code: #x06
> >             file code: #x06 (encoded by coding system utf-8-emacs)
> >               display: terminal code #x06
> >        hardcoded face: escape-glyph
> >
> > Character code properties: customize what to show
> >   old-name: ACKNOWLEDGE
> >   general-category: Cc (Other, Control)
> >
> > There are text properties here:
> >   fontified            t
> >
> > and the char that looks like ^L is:
> >
> >              position: 950 of 1750 (54%), restriction: <544-1751>, column: 0
> >             character: C-l (displayed as C-l) (codepoint 12, #o14, #xc)
> >               charset: ascii (ASCII (ISO646 IRV))
> > code point in charset: 0x0C
> >                script: latin
> >                syntax:          which means: whitespace
> >              to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"
> >           buffer code: #x0C
> >             file code: #x0C (encoded by coding system utf-8-emacs)
> >               display: terminal code #x0C
> >        hardcoded face: escape-glyph
> >
> > Character code properties: customize what to show
> >   old-name: FORM FEED (FF)
> >   general-category: Cc (Other, Control)
> >
> > There are text properties here:
> >   fontified            t
> >
>
> I find the clues: if I run `emacs -Q', the results will be the same as
> yours. If I run  `emacs', the problem reported here will happen. So
> the problem is triggered by some configurations in my
> `~/.emacs.d/init.el'. But I still can't find out the specific
> configuration which caused the problem.

I found the reason: it is caused by the following configuration:

```
(straight-use-package
 `(swiper :type git :host github :repo "abo-abo/swiper"
    :pre-build (
               ;("bash" "-c" "cd ~/.emacs.d/straight/repos/swiper")
               ;https://github.com/abo-abo/swiper/issues/2886#issuecomment-860605327
               ("make" "deps")
               ("make" "compile")
               )))

(require 'ivy)
(ivy-mode 1)
(setq ivy-use-virtual-buffers t)
(setq ivy-count-format "(%d/%d) ")
```

But I still can't figure out why this configuration will trigger the
above problem.

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Tue, Jul 6, 2021 at 7:22 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
>
> On Tue, Jul 6, 2021 at 7:07 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
> >
> > On Tue, Jul 6, 2021 at 6:46 PM Emanuel Berg via Users list for the GNU
> > Emacs text editor <help-gnu-emacs@gnu.org> wrote:
> > >
> > > Hongyi Zhao wrote:
> > >
> > > > The screenshot is generated by `C-x 8 RET c', but `M-x
> > > > describe-char RET' for the result character says that it
> > > > should be input by `C-x 8 RET 6', as you can see in the
> > > > screenshot. So, I'm confused on this problem.
> > >
> > > Here are mine, C-x 8 RET 6 RET
> > >
> > >
> > >
> > > and C-x 8 RET c RET
> > >
> > >
> > >
> > > and M-x insert-char RET form feed (ff) RET
> > >
> > >
> > >
> > > The char that looks like ^F is:
> > >
> > >              position: 894 of 959 (93%), restriction: <544-960>, column: 0
> > >             character: C-f (displayed as C-f) (codepoint 6, #o6, #x6)
> > >               charset: ascii (ASCII (ISO646 IRV))
> > > code point in charset: 0x06
> > >                script: latin
> > >                syntax: .        which means: punctuation
> > >              to input: type "C-x 8 RET 6" or "C-x 8 RET ACKNOWLEDGE"
> > >           buffer code: #x06
> > >             file code: #x06 (encoded by coding system utf-8-emacs)
> > >               display: terminal code #x06
> > >        hardcoded face: escape-glyph
> > >
> > > Character code properties: customize what to show
> > >   old-name: ACKNOWLEDGE
> > >   general-category: Cc (Other, Control)
> > >
> > > There are text properties here:
> > >   fontified            t
> > >
> > > and the char that looks like ^L is:
> > >
> > >              position: 950 of 1750 (54%), restriction: <544-1751>, column: 0
> > >             character: C-l (displayed as C-l) (codepoint 12, #o14, #xc)
> > >               charset: ascii (ASCII (ISO646 IRV))
> > > code point in charset: 0x0C
> > >                script: latin
> > >                syntax:          which means: whitespace
> > >              to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"
> > >           buffer code: #x0C
> > >             file code: #x0C (encoded by coding system utf-8-emacs)
> > >               display: terminal code #x0C
> > >        hardcoded face: escape-glyph
> > >
> > > Character code properties: customize what to show
> > >   old-name: FORM FEED (FF)
> > >   general-category: Cc (Other, Control)
> > >
> > > There are text properties here:
> > >   fontified            t
> > >
> >
> > I find the clues: if I run `emacs -Q', the results will be the same as
> > yours. If I run  `emacs', the problem reported here will happen. So
> > the problem is triggered by some configurations in my
> > `~/.emacs.d/init.el'. But I still can't find out the specific
> > configuration which caused the problem.
>
> I found the reason: it is caused by the following configuration:
>
> ```
> (straight-use-package
>  `(swiper :type git :host github :repo "abo-abo/swiper"
>     :pre-build (
>                ;("bash" "-c" "cd ~/.emacs.d/straight/repos/swiper")
>                ;https://github.com/abo-abo/swiper/issues/2886#issuecomment-860605327
>                ("make" "deps")
>                ("make" "compile")
>                )))
>
> (require 'ivy)
> (ivy-mode 1)
> (setq ivy-use-virtual-buffers t)
> (setq ivy-count-format "(%d/%d) ")
> ```
>
> But I still can't figure out why this configuration will trigger the
> above problem.

I've filed a bug report on <https://github.com/abo-abo/swiper/issues/2888>.

HY
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Tue, Jul 6, 2021 at 7:55 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
>
> On Tue, Jul 6, 2021 at 7:22 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
> >
> > On Tue, Jul 6, 2021 at 7:07 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
> > >
> > > On Tue, Jul 6, 2021 at 6:46 PM Emanuel Berg via Users list for the GNU
> > > Emacs text editor <help-gnu-emacs@gnu.org> wrote:
> > > >
> > > > Hongyi Zhao wrote:
> > > >
> > > > > The screenshot is generated by `C-x 8 RET c', but `M-x
> > > > > describe-char RET' for the result character says that it
> > > > > should be input by `C-x 8 RET 6', as you can see in the
> > > > > screenshot. So, I'm confused on this problem.
> > > >
> > > > Here are mine, C-x 8 RET 6 RET
> > > >
> > > >
> > > >
> > > > and C-x 8 RET c RET
> > > >
> > > >
> > > >
> > > > and M-x insert-char RET form feed (ff) RET
> > > >
> > > >
> > > >
> > > > The char that looks like ^F is:
> > > >
> > > >              position: 894 of 959 (93%), restriction: <544-960>, column: 0
> > > >             character: C-f (displayed as C-f) (codepoint 6, #o6, #x6)
> > > >               charset: ascii (ASCII (ISO646 IRV))
> > > > code point in charset: 0x06
> > > >                script: latin
> > > >                syntax: .        which means: punctuation
> > > >              to input: type "C-x 8 RET 6" or "C-x 8 RET ACKNOWLEDGE"
> > > >           buffer code: #x06
> > > >             file code: #x06 (encoded by coding system utf-8-emacs)
> > > >               display: terminal code #x06
> > > >        hardcoded face: escape-glyph
> > > >
> > > > Character code properties: customize what to show
> > > >   old-name: ACKNOWLEDGE
> > > >   general-category: Cc (Other, Control)
> > > >
> > > > There are text properties here:
> > > >   fontified            t
> > > >
> > > > and the char that looks like ^L is:
> > > >
> > > >              position: 950 of 1750 (54%), restriction: <544-1751>, column: 0
> > > >             character: C-l (displayed as C-l) (codepoint 12, #o14, #xc)
> > > >               charset: ascii (ASCII (ISO646 IRV))
> > > > code point in charset: 0x0C
> > > >                script: latin
> > > >                syntax:          which means: whitespace
> > > >              to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"
> > > >           buffer code: #x0C
> > > >             file code: #x0C (encoded by coding system utf-8-emacs)
> > > >               display: terminal code #x0C
> > > >        hardcoded face: escape-glyph
> > > >
> > > > Character code properties: customize what to show
> > > >   old-name: FORM FEED (FF)
> > > >   general-category: Cc (Other, Control)
> > > >
> > > > There are text properties here:
> > > >   fontified            t
> > > >
> > >
> > > I find the clues: if I run `emacs -Q', the results will be the same as
> > > yours. If I run  `emacs', the problem reported here will happen. So
> > > the problem is triggered by some configurations in my
> > > `~/.emacs.d/init.el'. But I still can't find out the specific
> > > configuration which caused the problem.
> >
> > I found the reason: it is caused by the following configuration:
> >
> > ```
> > (straight-use-package
> >  `(swiper :type git :host github :repo "abo-abo/swiper"
> >     :pre-build (
> >                ;("bash" "-c" "cd ~/.emacs.d/straight/repos/swiper")
> >                ;https://github.com/abo-abo/swiper/issues/2886#issuecomment-860605327
> >                ("make" "deps")
> >                ("make" "compile")
> >                )))
> >
> > (require 'ivy)
> > (ivy-mode 1)
> > (setq ivy-use-virtual-buffers t)
> > (setq ivy-count-format "(%d/%d) ")
> > ```
> >
> > But I still can't figure out why this configuration will trigger the
> > above problem.
>
> I've filed a bug report on <https://github.com/abo-abo/swiper/issues/2888>.

I also tried with helm, <https://github.com/emacs-helm/helm>, and
found that it also has the same problem.

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> I've filed a bug report on
> <https://github.com/abo-abo/swiper/issues/2888>.

Good!

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> But I still can't figure out why this configuration will
> trigger the above problem.

Indeed, why?

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Wed, Jul 7, 2021 at 12:25 AM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Hongyi Zhao wrote:
>
> > But I still can't figure out why this configuration will
> > trigger the above problem.
>
> Indeed, why?

See the following comment for detailed explanation:

 https://github.com/abo-abo/swiper/issues/2888#issuecomment-874791007

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

>>> But I still can't figure out why this configuration will
>>> trigger the above problem.
>>
>> Indeed, why?
>
> See the following comment for detailed explanation:
>
>  https://github.com/abo-abo/swiper/issues/2888#issuecomment-874791007

So it is Ivy's fault? I'm not a user of that so I'll pass...

--
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> I find the clues: if I run `emacs -Q'

The first thing one should do but never does. It is like the
advice the referee say to prize fighters before a bout,
"protect yourself at all times" :D

> the results will be the same as yours. If I run `emacs', the
> problem reported here will happen. So the problem is
> triggered by some configurations in my `~/.emacs.d/init.el'.
> But I still can't find out the specific configuration which
> caused the problem.

Do binary search :)

And use your intuition at the same time!

Even it it doesn't work you still get experience points to
level up later on...

And the more bugs, the faster you'll get there.

Hm...

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Wed, Jul 7, 2021 at 12:15 AM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Hongyi Zhao wrote:
>
> > I find the clues: if I run `emacs -Q'
>
> The first thing one should do but never does. It is like the
> advice the referee say to prize fighters before a bout,
> "protect yourself at all times" :D
>
> > the results will be the same as yours. If I run `emacs', the
> > problem reported here will happen. So the problem is
> > triggered by some configurations in my `~/.emacs.d/init.el'.
> > But I still can't find out the specific configuration which
> > caused the problem.
>
> Do binary search :)
>

The init file is a pure ASCII file, so why do you suggest this trick here?

> And use your intuition at the same time!
>
> Even it it doesn't work you still get experience points to
> level up later on...
>
> And the more bugs, the faster you'll get there.
>
> Hm...
>
> --
> underground experts united
> https://dataswamp.org/~incal
>
>


-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

>>> the results will be the same as yours. If I run `emacs',
>>> the problem reported here will happen. So the problem is
>>> triggered by some configurations in my
>>> `~/.emacs.d/init.el'. But I still can't find out the
>>> specific configuration which caused the problem.
>>
>> Do binary search :)
>>
>
> The init file is a pure ASCII file, so why do you suggest
> this trick here?

Binary search is a search algorithm and you can apply it,
manually, to your own Elisp to find an error if you have no
clue where it is. It doesn't take a lot of iterations to find
the error, usually.

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Tue, Jul 13, 2021 at 11:10 AM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Hongyi Zhao wrote:
>
> >>> the results will be the same as yours. If I run `emacs',
> >>> the problem reported here will happen. So the problem is
> >>> triggered by some configurations in my
> >>> `~/.emacs.d/init.el'. But I still can't find out the
> >>> specific configuration which caused the problem.
> >>
> >> Do binary search :)
> >>
> >
> > The init file is a pure ASCII file, so why do you suggest
> > this trick here?
>
> Binary search is a search algorithm and you can apply it,
> manually, to your own Elisp to find an error if you have no
> clue where it is. It doesn't take a lot of iterations to find
> the error, usually.

I misunderstood your meaning previously. Thank you for your
clarification. You're talking about the technique as described on
<https://rosettacode.org/wiki/Binary_search>.

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
No. 473, Quannan West Street, Xindu District, Xingtai, Hebei province

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> I misunderstood your meaning previously. Thank you for your
> clarification. You're talking about the technique as
> described on <https://rosettacode.org/wiki/Binary_search>.

You are welcome, interesting page BTW, they even have an Elisp
example, that uses `cl-do'.

-- 
underground experts united
https://dataswamp.org/~incal

Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Tue, Jul 6, 2021 at 12:07 PM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Hongyi Zhao wrote:
>
> > But `M-x describe-char RET' for `^L' in scratch buffer shows
> > the following:
> >
> > to input: type "C-x 8 RET c" or "C-x 8 RET FORM FEED (FF)"
> >
> > And the above-mentioned two type input sequences will
> > generated different characters:
> >
> > "C-x 8 RET c" --->  `^F'
> > "C-x 8 RET FORM FEED (FF)" --->  `^L'
>
> I get ^L for both of them

Why ^ is used to represent Ctrl?

Hongyi

RE: [External] : Re: The `^L' appeared in built-in help.

[Drew Adams]

> Why ^ is used to represent Ctrl?

First Duck-Duck hit for _exactly_ your text:

https://unix.stackexchange.com/questions/265245/why-is-the-circumflex-caret-character-used-as-a-symbol-for-ctrl

Re: [External] : Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Tue, Jul 20, 2021 at 9:42 AM Drew Adams <drew.adams@oracle.com> wrote:
>
> > Why ^ is used to represent Ctrl?
>
> First Duck-Duck hit for _exactly_ your text:
>
> https://unix.stackexchange.com/questions/265245/why-is-the-circumflex-caret-character-used-as-a-symbol-for-ctrl

Asking google with "Why ^ is used to represent Ctrl?" give me the following:

https://retrocomputing.stackexchange.com/questions/10925/why-do-we-use-caret-as-the-symbol-for-ctrl-control

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
No. 473, Quannan West Street, Xindu District, Xingtai, Hebei province

RE: [External] : Re: The `^L' appeared in built-in help.

[Drew Adams]

> Asking google with "Why ^ is used to represent Ctrl?" give me the following:
> 
> https://retrocomputing.stackexchange.com/questions/10925/why-do-we-use-caret-as-the-symbol-for-ctrl-control

Yes.  That wasn't so hard, was it?

Re: [External] : Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

Yeah.

On Tue, Jul 20, 2021 at 12:28 PM Drew Adams <drew.adams@oracle.com> wrote:
>
> > Asking google with "Why ^ is used to represent Ctrl?" give me the following:
> >
> > https://retrocomputing.stackexchange.com/questions/10925/why-do-we-use-caret-as-the-symbol-for-ctrl-control
>
> Yes.  That wasn't so hard, was it?



-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
No. 473, Quannan West Street, Xindu District, Xingtai, Hebei province

Re: [External] : Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

[-- Attachment #1: Type: text/plain, Size: 433 bytes --]

Another issue: what's the regexp for matching the `^L' in Emacs. I
tried with `^.*\^L$' to filter the counsel-unicode-char command's
results, but nothing is matched. See the attachment for the detailed
info.

Regards
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
No. 473, Quannan West Street, Xindu District, Xingtai, Hebei province

[-- Attachment #2: counsel-unicode-char-form-feed.png --]
[-- Type: image/png, Size: 115585 bytes --]

[-- Attachment #3: form-feed.png --]
[-- Type: image/png, Size: 113139 bytes --]

RE: [External] : Re: The `^L' appeared in built-in help.

[Drew Adams]

> Another issue: what's the regexp for matching the `^L' in Emacs. I
> tried with `^.*\^L$' to filter the counsel-unicode-char command's
> results, but nothing is matched. See the attachment for the detailed
> info.

The regexp for matching a Control-L character in Emacs
is a Control-L character.

M-: ( search-forward C-q C-l )    ; Lisp
M-: ( re-search-forward C-q C-l )

C-s C-q C-l                       ; Isearch

I can't speak to what Counsel expects from you.

https://www.gnu.org/software/emacs/manual/html_node/emacs/Inserting-Text.html

Re: [External] : Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> Another issue: what's the regexp for matching the `^L' in
> Emacs. I tried with `^.*\^L$' to filter the
> counsel-unicode-char command's results, but nothing
> is matched.

^ in the beginning of a regexp means the beginning of a line.

(search-forward-regexp "^aaa") ; works

aaa

(search-forward-regexp "^aaa") ; DNC

 aaa

(search-forward-regexp "^a^aa") ; works

a^aa

(search-forward-regexp "\\^aaa") ; works

^aaa

But to answer your question:

(search-forward-regexp "\f")

\f

-- 
underground experts united
https://dataswamp.org/~incal

Re: [External] : Re: The `^L' appeared in built-in help.

[Hongyi Zhao]

On Wed, Jul 21, 2021 at 12:32 AM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Hongyi Zhao wrote:
>
> > Another issue: what's the regexp for matching the `^L' in
> > Emacs. I tried with `^.*\^L$' to filter the
> > counsel-unicode-char command's results, but nothing
> > is matched.
>
> ^ in the beginning of a regexp means the beginning of a line.
>
> (search-forward-regexp "^aaa") ; works
>
> aaa
>
> (search-forward-regexp "^aaa") ; DNC
>
>  aaa
>
> (search-forward-regexp "^a^aa") ; works
>
> a^aa
>
> (search-forward-regexp "\\^aaa") ; works
>
> ^aaa
>
> But to answer your question:
>
> (search-forward-regexp " ")

What does this mean? I mean, I don't want to match a blank space here,
as you suggested above.

HY

Re: [External] : Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

>> (search-forward-regexp " ")
>
> What does this mean? I mean, I don't want to match a blank
> space here, as you suggested above.

It turns up like that, it should be a ^L.

  M-x insert-char RET form feed (ff) RET

-- 
underground experts united
https://dataswamp.org/~incal

RE: [External] : Re: The `^L' appeared in built-in help.

[Drew Adams]

[-- Attachment #1: Type: text/plain, Size: 146 bytes --]

> M-x insert-char RET form feed (ff) RET

aka:

`C-q C-l'

https://www.gnu.org/software/emacs/manual/html_node/emacs/Inserting-Text.html


[-- Attachment #2: winmail.dat --]
[-- Type: application/ms-tnef, Size: 14265 bytes --]

Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Hongyi Zhao]

On Wed, Jul 21, 2021 at 12:44 PM Drew Adams <drew.adams@oracle.com> wrote:
>
> > M-x insert-char RET form feed (ff) RET
>
> aka:
>
> `C-q C-l'
>
> https://www.gnu.org/software/emacs/manual/html_node/emacs/Inserting-Text.html

If I don't know the Unicode name and the above input sequence of it,
to be more specifically, I only know its representation in Emacs is
^L, then how to search/match/find/filter out it with regexp.

As a similar example, I can grep it with the following

$ grep $'\014' 11.txt | cat -te
^L$
$ grep $'\f' 11.txt | cat -te
^L$


-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
No. 473, Quannan West Street, Xindu District, Xingtai, Hebei province

RE: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Drew Adams]

> > > M-x insert-char RET form feed (ff) RET
> >
> > aka:
> >
> > `C-q C-l'
> >
> > https://www.gnu.org/software/emacs/manual/html_node/emacs/Inserting-Text.html
> 
> If I don't know the Unicode name and the above input sequence of it,
> to be more specifically, I only know its representation in Emacs is
> ^L, then how to search/match/find/filter out it with regexp.
> 
> As a similar example, I can grep it with the following
> 
> $ grep $'\014' 11.txt | cat -te
> ^L$
> $ grep $'\f' 11.txt | cat -te
> ^L$

It's not clear (to me) what you're trying to do.
The initial question was about _inserting_ the char, I believe.
For that, `C-q' is the easiest way for a control char, since
you can just hit the key for the control char (`C-l' in this case).

For other Unicode chars, `M-x insert-char' can help, but you don't
need that just to insert an ASCII control char.

Now you seem to be asking something else, and what it is is not
clear to me.  If you're asking about search, then just use `C-q':
`C-s C-q C-l'

Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Hongyi Zhao]

On Thu, Jul 22, 2021 at 1:08 AM Drew Adams <drew.adams@oracle.com> wrote:
>
> > > > M-x insert-char RET form feed (ff) RET
> > >
> > > aka:
> > >
> > > `C-q C-l'
> > >
> > > https://www.gnu.org/software/emacs/manual/html_node/emacs/Inserting-Text.html
> >
> > If I don't know the Unicode name and the above input sequence of it,
> > to be more specifically, I only know its representation in Emacs is
> > ^L, then how to search/match/find/filter out it with regexp.
> >
> > As a similar example, I can grep it with the following
> >
> > $ grep $'\014' 11.txt | cat -te
> > ^L$
> > $ grep $'\f' 11.txt | cat -te
> > ^L$
>
> It's not clear (to me) what you're trying to do.
> The initial question was about _inserting_ the char, I believe.
> For that, `C-q' is the easiest way for a control char, since
> you can just hit the key for the control char (`C-l' in this case).

As I've recapped the title of the issue, I've made another slightly
different discussion from the OP, i.e., searching the document with
regexp for matching the control characters.

> For other Unicode chars, `M-x insert-char' can help, but you don't
> need that just to insert an ASCII control char.
>
> Now you seem to be asking something else, and what it is is not
> clear to me.  If you're asking about search,

Yes, that's what I'm concerned about

> then just use `C-q':
> `C-s C-q C-l'

I want to know whether there are some similar regexp patterns in Emacs
as the ones used by grep, say, $'\014' or $'\f'.

HY

Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Emanuel Berg via Users list for the GNU Emacs text editor]

Hongyi Zhao wrote:

> I want to know whether there are some similar regexp
> patterns in Emacs as the ones used by grep, say, $'\014' or
> $'\f'.

(when (re-search-forward "\C-l")
  (replace-match "do it today, in a different way") )

^L

-- 
underground experts united
https://dataswamp.org/~incal

RE: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Drew Adams]

[-- Attachment #1: Type: text/plain, Size: 247 bytes --]

> > I want to know whether there are some similar regexp
> > patterns in Emacs as the ones used by grep, say, $'\014' or
> > $'\f'.
> 
> (re-search-forward "\C-l")

Yes, or (re-search-forward "[\f]")
     or (re-search-forward "[\014]")


[-- Attachment #2: winmail.dat --]
[-- Type: application/ms-tnef, Size: 14919 bytes --]

Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Emanuel Berg via Users list for the GNU Emacs text editor]

Drew Adams wrote:

>>> I want to know whether there are some similar regexp
>>> patterns in Emacs as the ones used by grep, say, $'\014'
>>> or $'\f'.
>> 
>> (re-search-forward "\C-l")
>
> Yes, or (re-search-forward "[\f]")
>      or (re-search-forward "[\014]")

What about

  (re-search-forward (kbd "C-l"))

?

-- 
underground experts united
https://dataswamp.org/~incal

RE: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Drew Adams]

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> >>> I want to know whether there are some similar regexp
> >>> patterns in Emacs as the ones used by grep, say, $'\014'
> >>> or $'\f'.
> >>
> >> (re-search-forward "\C-l")
> >
> > Yes, or (re-search-forward "[\f]")
> >      or (re-search-forward "[\014]")
> 
> What about
> 
>   (re-search-forward (kbd "C-l"))

Sure.  Which is the same as (re-search-forward "\f").

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Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Emanuel Berg via Users list for the GNU Emacs text editor]

Drew Adams wrote:

>>>>> I want to know whether there are some similar regexp
>>>>> patterns in Emacs as the ones used by grep, say, $'\014'
>>>>> or $'\f'.
>>>>
>>>> (re-search-forward "\C-l")
>>>
>>> Yes, or (re-search-forward "[\f]")
>>>      or (re-search-forward "[\014]")
>> 
>> What about
>> 
>>   (re-search-forward (kbd "C-l"))
>
> Sure.  Which is the same as (re-search-forward "\f").

So far, these works

  (re-search-forward "[\014]")
  (re-search-forward "[\f]")
  (re-search-forward "\C-l")
  (re-search-forward "\f")
  (re-search-forward (kbd "C-l"))

It seems subexpressions at lines 1 and 2 evaluate to the same
"[^L]", as does for their part lines 3, 4 and 5, and then it
is "^L"...

\f

-- 
underground experts united
https://dataswamp.org/~incal

Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Hongyi Zhao]

On Thu, Jul 22, 2021 at 12:14 PM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Drew Adams wrote:
>
> >>>>> I want to know whether there are some similar regexp
> >>>>> patterns in Emacs as the ones used by grep, say, $'\014'
> >>>>> or $'\f'.
> >>>>
> >>>> (re-search-forward "\C-l")
> >>>
> >>> Yes, or (re-search-forward "[\f]")
> >>>      or (re-search-forward "[\014]")
> >>
> >> What about
> >>
> >>   (re-search-forward (kbd "C-l"))
> >
> > Sure.  Which is the same as (re-search-forward "\f").
>
> So far, these works
>
>   (re-search-forward "[\014]")
>   (re-search-forward "[\f]")
>   (re-search-forward "\C-l")
>   (re-search-forward "\f")
>   (re-search-forward (kbd "C-l"))
>
> It seems subexpressions at lines 1 and 2 evaluate to the same
> "[^L]", as does for their part lines 3, 4 and 5, and then it
> is "^L"...

I observed the same behavior.

HY
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
No. 473, Quannan West Street, Xindu District, Xingtai, Hebei province

Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Hongyi Zhao]

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On Thu, Jul 22, 2021 at 12:14 PM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Drew Adams wrote:
>
> >>>>> I want to know whether there are some similar regexp
> >>>>> patterns in Emacs as the ones used by grep, say, $'\014'
> >>>>> or $'\f'.
> >>>>
> >>>> (re-search-forward "\C-l")
> >>>
> >>> Yes, or (re-search-forward "[\f]")
> >>>      or (re-search-forward "[\014]")
> >>
> >> What about
> >>
> >>   (re-search-forward (kbd "C-l"))
> >
> > Sure.  Which is the same as (re-search-forward "\f").
>
> So far, these works
>
>   (re-search-forward "[\014]")
>   (re-search-forward "[\f]")
>   (re-search-forward "\C-l")
>   (re-search-forward "\f")
>   (re-search-forward (kbd "C-l"))
>
> It seems subexpressions at lines 1 and 2 evaluate to the same
> "[^L]", as does for their part lines 3, 4 and 5, and then it
> is "^L"...

I observed another strange phenomenon as described below.

Suppose I've the following content in scratch buffer:

(re-search-forward "\f")
^L

I put the point at the end of sexp line, and hit `C-j' to evaluate it.
I find that each time after the sexp has been evaluated successfully,
the `^L' line will be moved to the next line. See the screenshot in
the attachment, where I've evaluated the sexp 4 times.

Any hints for this behavior?

Regards,
HY

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Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[tomas]

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On Thu, Jul 22, 2021 at 09:56:09PM +0800, Hongyi Zhao wrote:

[...]

> Suppose I've the following content in scratch buffer:
> 
> (re-search-forward "\f")
> ^L
> 
> I put the point at the end of sexp line, and hit `C-j' to evaluate it.
> I find that each time after the sexp has been evaluated successfully,
> the `^L' line will be moved to the next line. See the screenshot in
> the attachment, where I've evaluated the sexp 4 times.
> 
> Any hints for this behavior?

That depends on what C-j is bound to. What does say "describe-key",
aka C-h C-k?

Cheers
 - t

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Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Hongyi Zhao]

On Thu, Jul 22, 2021 at 10:38 PM <tomas@tuxteam.de> wrote:
>
> On Thu, Jul 22, 2021 at 09:56:09PM +0800, Hongyi Zhao wrote:
>
> [...]
>
> > Suppose I've the following content in scratch buffer:
> >
> > (re-search-forward "\f")
> > ^L
> >
> > I put the point at the end of sexp line, and hit `C-j' to evaluate it.
> > I find that each time after the sexp has been evaluated successfully,
> > the `^L' line will be moved to the next line. See the screenshot in
> > the attachment, where I've evaluated the sexp 4 times.
> >
> > Any hints for this behavior?
>
> That depends on what C-j is bound to. What does say "describe-key",
> aka C-h C-k?

`C-h k C-j RET':
;;;
C-j runs the command eval-print-last-sexp (found in
lisp-interaction-mode-map), which is an interactive compiled Lisp
function in ‘elisp-mode.el’.

It is bound to C-j, <menu-bar> <lisp-interaction> <Evaluate and
Print>.
[...]
;;;

Best,
HY

Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[tomas]

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On Thu, Jul 22, 2021 at 10:53:53PM +0800, Hongyi Zhao wrote:
> On Thu, Jul 22, 2021 at 10:38 PM <tomas@tuxteam.de> wrote:
> >
> > On Thu, Jul 22, 2021 at 09:56:09PM +0800, Hongyi Zhao wrote:
> >
> > [...]
> >
> > > Suppose I've the following content in scratch buffer:
> > >
> > > (re-search-forward "\f")
> > > ^L
> > >
> > > I put the point at the end of sexp line, and hit `C-j' to evaluate it.
> > > I find that each time after the sexp has been evaluated successfully,
> > > the `^L' line will be moved to the next line. See the screenshot in
> > > the attachment, where I've evaluated the sexp 4 times.
> > >
> > > Any hints for this behavior?
> >
> > That depends on what C-j is bound to. What does say "describe-key",
> > aka C-h C-k?
> 
> `C-h k C-j RET':
> ;;;
> C-j runs the command eval-print-last-sexp (found in
> lisp-interaction-mode-map), which is an interactive compiled Lisp
> function in ‘elisp-mode.el’.

Ah. You seem to be in a "lisp interaction" buffer. Then it's clear:
it's the `print' part of `eval-print-last-sexp' what is inserting
stuff in your buffer: the value of (re-search-forward "\f").

Before it does a newline (that is what moves the ^L forward), then the
searching and moving of point happens, then (you should see that, too,
the expression's value (point's position, an integer) is inserted: you
should get a number after the ^L, too.

Cheers
 - t

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Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Hongyi Zhao]

On Thu, Jul 22, 2021 at 11:01 PM <tomas@tuxteam.de> wrote:
>
> On Thu, Jul 22, 2021 at 10:53:53PM +0800, Hongyi Zhao wrote:
> > On Thu, Jul 22, 2021 at 10:38 PM <tomas@tuxteam.de> wrote:
> > >
> > > On Thu, Jul 22, 2021 at 09:56:09PM +0800, Hongyi Zhao wrote:
> > >
> > > [...]
> > >
> > > > Suppose I've the following content in scratch buffer:
> > > >
> > > > (re-search-forward "\f")
> > > > ^L
> > > >
> > > > I put the point at the end of sexp line, and hit `C-j' to evaluate it.
> > > > I find that each time after the sexp has been evaluated successfully,
> > > > the `^L' line will be moved to the next line. See the screenshot in
> > > > the attachment, where I've evaluated the sexp 4 times.
> > > >
> > > > Any hints for this behavior?
> > >
> > > That depends on what C-j is bound to. What does say "describe-key",
> > > aka C-h C-k?
> >
> > `C-h k C-j RET':
> > ;;;
> > C-j runs the command eval-print-last-sexp (found in
> > lisp-interaction-mode-map), which is an interactive compiled Lisp
> > function in ‘elisp-mode.el’.
>
> Ah. You seem to be in a "lisp interaction" buffer.

I'm in scratch buffer, and the "lisp interaction" is its default major mode.

> Then it's clear:
> it's the `print' part of `eval-print-last-sexp' what is inserting
> stuff in your buffer: the value of (re-search-forward "\f").
>
> Before it does a newline (that is what moves the ^L forward), then the
> searching and moving of point happens, then (you should see that, too,
> the expression's value (point's position, an integer) is inserted: you
> should get a number after the ^L, too.

Thank you for your explanation.

Best,
HY

Re: [External] : Re: Regexp for matching control character, say, FORM FEED.

[Michael Heerdegen]

Hongyi Zhao <hongyi.zhao@gmail.com> writes:

> C-j runs the command eval-print-last-sexp (found in
> lisp-interaction-mode-map), which is an interactive compiled Lisp
> function in ‘elisp-mode.el’.

C-x C-e if you only want to see the result in the echo area.

Michael.

Re: [External] : Re: Regexp for matching control character, say, FORM FEED.

[Hongyi Zhao]

On Fri, Jul 23, 2021 at 6:08 AM Michael Heerdegen
<michael_heerdegen@web.de> wrote:
>
> Hongyi Zhao <hongyi.zhao@gmail.com> writes:
>
> > C-j runs the command eval-print-last-sexp (found in
> > lisp-interaction-mode-map), which is an interactive compiled Lisp
> > function in ‘elisp-mode.el’.
>
> C-x C-e if you only want to see the result in the echo area.

Thank you for your comment. It does the trick with the point at the
end of the sexp, and the info similar to the following will be shown
in the minibuffer:

172 (#o254, #xac)

Hongyi
-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
No. 473, Quannan West Street, Xindu District, Xingtai, Hebei province

RE: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Drew Adams]

> > So far, these works
> >
> >   (re-search-forward "[\014]")
> >   (re-search-forward "[\f]")
> >   (re-search-forward "\C-l")
> >   (re-search-forward "\f")
> >   (re-search-forward (kbd "C-l"))
> >
> > It seems subexpressions at lines 1 and 2 evaluate to the same
> > "[^L]", as does for their part lines 3, 4 and 5, and then it
> > is "^L"...
> 
> I observed another strange phenomenon as described below.
             ^^^^^^^

None of the above is a "strange phenomenon".  It's
normal, helpful, and well documented.

> Any hints for this behavior?

Well explained by Thomas.

And it has nothing to do with the form-feed (C-l)
character. `re-search-forward' returns the value of
`point' when it's done; and that value is printed.

Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[tomas]

[-- Attachment #1: Type: text/plain, Size: 476 bytes --]

On Thu, Jul 22, 2021 at 05:07:36PM +0000, Drew Adams wrote:

[Hongyi Zhao]

> > I observed another strange phenomenon as described below.
>              ^^^^^^^
> 
> None of the above is a "strange phenomenon".  It's
> normal, helpful, and well documented.

Beauty is always in the eye of the beholder. Strangeness and charm
probably too :-)

I must admit that I'm often charmed, fascinated and dumbfounded at
the results my programs produce...

Cheers
 - t

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Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Emanuel Berg via Users list for the GNU Emacs text editor]

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tomas wrote:

> I must admit that I'm often charmed, fascinated and
> dumbfounded at the results my programs produce...

https://dataswamp.org/~incal/figures/opengl-glsl/opengl4.png


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-- 
underground experts united
https://dataswamp.org/~incal

Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[tomas]

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On Thu, Jul 22, 2021 at 09:13:31AM +0800, Hongyi Zhao wrote:

[...]

> I want to know whether there are some similar regexp patterns in Emacs
> as the ones used by grep, say, $'\014' or $'\f'.

To offer some other perspective on the (correct) answers by Emanuel and
Drew, remember that a regular expression is, basically, a string
where each character is interpreted as "itself", unless it is a "regexp
special" character [1]. So, for example searching for the regular expression
"a" will find all "a"s in your text, because the character a isn't a
"regexp special".

Now ASCII control characters are all *not* "regexp special" so you only
have to find a way to express them whithin a string. How, that is stated
in the Emacs Lisp manual when it talks about "string type" [2] (especially
the subnode "Non-ASCII Characters in Strings", which leads you to "character
type" [3]. The special forms "\f", "\^L" or "\C-L" (all of them equivalent),
which all were talked about here are treated in a subnode of the above [4].
This notation carries some historical baggage, so don't expect too much
logic from it.

For example, why ^L? Because form feed is at point 12 (in decimal) in the
ascii table, and L at point 76, the difference being 64. What happens is
that the "^" "subtracts 64 from the character code", or more precisely
masks out bit 6 of its binary representation. So ^M would be "carriage
return" and so on. Just have a look at the ASCII table.

Then "\f" comes from the C string literal representation. It's meant to
be mnemonic ("f" for "form feed" -- similarly "\n" for "line feed", aka
"new line", "\b" for "bell" and so on).

The references below lead you to more alternative representations, like
short hex "\x0C", short Unicode hex "\u000C", long Unicode hex "\U0000000C";
there are also (mostly historical) octals, etc.

You can even put the unicode /names/ in there, using the "\N{...}"
notation, so your ^L can be named "\N{FORM FEED (FF)}" (yes the (FF)
in parentheses is part of it: the Unicode Consortium put it in there.
Life is like that).

If you want to explore those unicode names, type in C-x 8 <RET>, you
can autocomplete your way among them.

Hope this gives some rough map for that landscape :-)

Cheers

[1] Emacs Lisp reference manual "Syntax of Regular Expressions"
    or https://www.gnu.org/software/emacs/manual/html_node/elisp/Syntax-of-Regexps.html


[2] Emacs Lisp reference manual "String Type" and its subnodes
    or https://www.gnu.org/software/emacs/manual/html_node/elisp/String-Type.html
    
[3] Emacs Lisp reference manual "Character Type"
    https://www.gnu.org/software/emacs/manual/html_node/elisp/Character-Type.html

[4] Emacs Lisp reference manual "Control-Character Syntax"
    https://www.gnu.org/software/emacs/manual/html_node/elisp/Ctl_002dChar-Syntax.html

 - tomás

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Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Hongyi Zhao]

On Thu, Jul 22, 2021 at 4:06 PM <tomas@tuxteam.de> wrote:
>
> On Thu, Jul 22, 2021 at 09:13:31AM +0800, Hongyi Zhao wrote:
>
> [...]
>
> > I want to know whether there are some similar regexp patterns in Emacs
> > as the ones used by grep, say, $'\014' or $'\f'.
>
> To offer some other perspective on the (correct) answers by Emanuel and
> Drew, remember that a regular expression is, basically, a string
> where each character is interpreted as "itself", unless it is a "regexp
> special" character [1]. So, for example searching for the regular expression
> "a" will find all "a"s in your text, because the character a isn't a
> "regexp special".
>
> Now ASCII control characters are all *not* "regexp special" so you only
> have to find a way to express them whithin a string. How, that is stated
> in the Emacs Lisp manual when it talks about "string type" [2] (especially
> the subnode "Non-ASCII Characters in Strings", which leads you to "character
> type" [3]. The special forms "\f", "\^L" or "\C-L" (all of them equivalent),
> which all were talked about here are treated in a subnode of the above [4].
> This notation carries some historical baggage, so don't expect too much
> logic from it.
>
> For example, why ^L? Because form feed is at point 12 (in decimal) in the
> ascii table, and L at point 76, the difference being 64.

$ man ascii |egrep  ' L$'
       014   12    0C    FF  '\f' (form feed)        114   76    4C    L

> What happens is that the "^" "subtracts 64 from the character code", or more precisely
> masks out bit 6 of its binary representation.

$ man ascii |egrep  ' \^$'
       036   30    1E    RS  (record separator)      136   94    5E    ^

If so, the RS should be represented by ^^ in a self-consistent way :-)

> So ^M would be "carriage return" and so on. Just have a look at the ASCII table.

$ man ascii |egrep  ' M$'
       015   13    0D    CR  '\r' (carriage ret)     115   77    4D    M


> Then "\f" comes from the C string literal representation. It's meant to
> be mnemonic ("f" for "form feed" -- similarly "\n" for "line feed", aka
> "new line", "\b" for "bell" and so on).
>
> The references below lead you to more alternative representations, like
> short hex "\x0C", short Unicode hex "\u000C", long Unicode hex "\U0000000C";
> there are also (mostly historical) octals, etc.
>
> You can even put the unicode /names/ in there, using the "\N{...}"
> notation, so your ^L can be named "\N{FORM FEED (FF)}" (yes the (FF)
> in parentheses is part of it: the Unicode Consortium put it in there.
> Life is like that).
>
> If you want to explore those unicode names, type in C-x 8 <RET>, you
> can autocomplete your way among them.
>
> Hope this gives some rough map for that landscape :-)

Thank you for your systematic and informative comments and explanations.

> Cheers
>
> [1] Emacs Lisp reference manual "Syntax of Regular Expressions"
>     or https://www.gnu.org/software/emacs/manual/html_node/elisp/Syntax-of-Regexps.html
>
>
> [2] Emacs Lisp reference manual "String Type" and its subnodes
>     or https://www.gnu.org/software/emacs/manual/html_node/elisp/String-Type.html
>
> [3] Emacs Lisp reference manual "Character Type"
>     https://www.gnu.org/software/emacs/manual/html_node/elisp/Character-Type.html
>
> [4] Emacs Lisp reference manual "Control-Character Syntax"
>     https://www.gnu.org/software/emacs/manual/html_node/elisp/Ctl_002dChar-Syntax.html
>
>  - tomás

Best,
HY

Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[tomas]

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On Thu, Jul 22, 2021 at 05:45:36PM +0800, Hongyi Zhao wrote:
> On Thu, Jul 22, 2021 at 4:06 PM <tomas@tuxteam.de> wrote:
> >
> > On Thu, Jul 22, 2021 at 09:13:31AM +0800, Hongyi Zhao wrote:

[...]

> If so, the RS should be represented by ^^ in a self-consistent way :-)

It is, indeed.

I can't enter it here interactively with the "C-q" trick, because my
keyboard setup maps it to a dead key (useful for entering accents),
but doing (insert "\^^") in an Emacs buffer and querying the result
with "describe character confirms that.

Note the fancy Unicode name "INFORMATION SEPARATOR TWO". For whatever
reason they chose that one alternative [1]. Perhaps because it sounds
more bureaucratic ;-)

Cheers

[1] https://en.wikipedia.org/wiki/C0_and_C1_control_codes#Category-Number_names

 - t

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Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Hongyi Zhao]

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On Thu, Jul 22, 2021 at 6:06 PM <tomas@tuxteam.de> wrote:
>
> On Thu, Jul 22, 2021 at 05:45:36PM +0800, Hongyi Zhao wrote:
> > On Thu, Jul 22, 2021 at 4:06 PM <tomas@tuxteam.de> wrote:
> > >
> > > On Thu, Jul 22, 2021 at 09:13:31AM +0800, Hongyi Zhao wrote:
>
> [...]
>
> > If so, the RS should be represented by ^^ in a self-consistent way :-)
>
> It is, indeed.
>
> I can't enter it here interactively with the "C-q" trick, because my
> keyboard setup maps it to a dead key (useful for entering accents),
> but doing (insert "\^^") in an Emacs buffer and querying the result
> with "describe character confirms that.
>
> Note the fancy Unicode name "INFORMATION SEPARATOR TWO". For whatever
> reason they chose that one alternative [1]. Perhaps because it sounds
> more bureaucratic ;-)
>
> Cheers
>
> [1] https://en.wikipedia.org/wiki/C0_and_C1_control_codes#Category-Number_names

Also see my screenshot shown by counsel-unicode-char command [1].

[1] https://github.com/abo-abo/swiper/blob/56139df678d9886d0612c0a192cce2cf6f156628/counsel.el#L5373

Best,
HY

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Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[tomas]

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On Thu, Jul 22, 2021 at 06:27:05PM +0800, Hongyi Zhao wrote:

[...]

> [1] https://github.com/abo-abo/swiper/blob/56139df678d9886d0612c0a192cce2cf6f156628/counsel.el#L5373

Didn't know about counsel, thanks for the pointer

Cheers
 - t

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Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)

[Emanuel Berg via Users list for the GNU Emacs text editor]

tomas wrote:

> For example, why ^L? Because form feed is at point 12 (in
> decimal) in the ascii table, and L at point 76, the
> difference being 64. What happens is that the "^" "subtracts
> 64 from the character code", or more precisely masks out bit
> 6 of its binary representation.

Cool :)

$ ascii -t L @ ff | awk '{print $5}'
01001100
01000000
00001100

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Re: The `^L' appeared in built-in help.

[2QdxY4RzWzUUiLuE]

On 2021-07-06 at 10:34:36 +0800,
Hongyi Zhao <hongyi.zhao@gmail.com> wrote:

> I noticed so many `^L' appeared in Emacs' built-in help. According to
> the ascii document shown below, this should mean '\f' (form feed):
> 
> $ man ascii | grep ' L$'
>        014   12    0C    FF  '\f' (form feed)        114   76    4C    L
> 
> But I also noticed that this control character is not used evenly
> throughout the document.
> 
> Any hints for this phenomenon?

When printed (yes, printed, on dead trees), those are page breaks (i.e.,
a command to continue printing on a new page).  Also, Emacs has "page"
commands (e.g., count-lines-page, forward-page) that work on "page"s of
text between page breaks.

This seems to hage come up recently as well; perhaps this list's archive
has more information.

Re: The `^L' appeared in built-in help.

[Emanuel Berg via Users list for the GNU Emacs text editor]

2QdxY4RzWzUUiLuE wrote:

> This seems to have come up recently as well; perhaps this
> list's archive has more information.

Maybe one should compile a FAQ, not a FAQ to reflect Emacs (I
doubt anyone would have included this question no matter how
many times it was asked) but the gmane.emacs.help Emacs user
subset and the questions that come up here?

It could be hyperlinks to old posts, even. And/or quotes.

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underground experts united
https://dataswamp.org/~incal