Thanks, Timothy and Max. I'll try to explain myself better.

Overlining is quite useful in math expressions, for example I needed it to represent the arithmetic mean.

I need to be able to overline text and to export it overlined. The only dirty solution I found was to change the =verbatim= mark, but now I can't use verbatim on orgmode, and the overlined text isn't exported, so unsustainable "solution".

The perfect solution? To be able to add a new marker to overline text that can be exported overlined.

Best regards

:-)

Message: 7
Date: Sat, 18 Sep 2021 20:48:36 +0800
From: Timothy <tecosaur@gmail.com>
To: Ypo <ypuntot@gmail.com>
Cc: emacs-orgmode@gnu.org
Subject: Re: Overlining troubles
Message-ID: <87ee9mdp5i.fsf@gmail.com>
Content-Type: text/plain; charset="utf-8"

Hi Ypo,

You’ll likely want to override `org-html-verbatim' and `org-latex-verbatim' to
produce overlines in exports.

All the best,
Timothy
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Message: 8
Date: Sat, 18 Sep 2021 19:50:31 +0700
From: Max Nikulin <manikulin@gmail.com>
To: emacs-orgmode@gnu.org
Subject: Re: Overlining troubles
Message-ID: <si4naq$47d$1@ciao.gmane.io>
Content-Type: text/plain; charset=utf-8; format=flowed

On 18/09/2021 15:14, Ypo wrote:

I have tried many times in different ways to "overline" text. I am able 
to overline it on orgmode (I sacrificed the =verbatim= marker to achieve 
it), but it doesn't export overlined (nor HTML, nor LaTeX).

I tried in the past to add it to "Org Emphasis Alist" but it didn't work.

Is it possible to add overlining and to export it?

Just to avoid confusion, `org-emphasis-alist' is not designed to change 
or to *add* new markers:

https://orgmode.org/list/87blatodir.fsf@nicolasgoaziou.fr/ (Nicolas 
Goaziou, Mon, 05 Apr 2021 01:06:52 +0200, Re: Using backticks for the 
inline code delimeter?)

If you wish to export =verbatim= text as text with line above, perhaps, 
you can define custom "verbatim" export filter
"info (org) Advanced Export Configuration"
https://orgmode.org/manual/Advanced-Export-Configuration.html

A macro expanded with markup for particular backend (e.g. @@latex: 
...@@) may be a better option
"info (org) Macro Replacement"
https://orgmode.org/manual/Macro-Replacement.html

Some people experimenting with custom link types with associated 
handlers for particular export backends:
https://orgmode.org/list/87mtq9zatr.fsf@posteo.net/ (Juan Manuel Macías, 
Mon, 26 Jul 2021 09:25:04 +0000, Multilingual quotes inside paragraphs).

Unfortunately you described what you have tried in too general words to 
suggest something more specific.