bug#31273: 27.0.50; org: #+begin_right block is not exported correctly

[Nicolas Goaziou <mail@nicolasgoaziou.fr>]

Dmitry Alexandrov <321942@gmail.com> writes:

> Just another unofficial reference card [0], by Caio Rordrigues at that time, that again states that:
>
> #+begin_right This text is aligned to the right! #+end_right
>
> These persons are probably consider themselves highly familiar with
> Org, yet they have been mistaken. What to say about novices! So the
> absence of this feature is indeed highly unobvious. That’s the only
> point I am trying to make.
>
> [0] https://github.com/caiorss/Emacs-Elisp-Programming/blob/master/Org-Mode.org#text-position
>
>> In any case, let me insist again on the following point: you can use
>> "#+begin_right" in HTML to your heart's content if you define the
>> appropriate CSS property.
>
> If there is no plan to make into default as with centring, a warning
> might be very apt.

The issue here is that "#+begin_right" is perfectly valid syntax, and so
is, e.g., "#+begin_foobar". Their behaviour is perfectly defined. For
example, in HTML export the will create <div class="right"> and <div
class="foobar"> if you have a nil `org-html-html5-fancy', or <right> and
<foobar> otherwise.

Therefore, a warning is not an option here. Only a careful read of the
manual can help clearing the misconception about what is included in Org
and what can be extended.

Now, it's true that at some point, Org defined a ".right" CSS rule
instead of ".org-right", so "#+begin_right" could work out of the box, but
only in the HTML export. However, this was not the intent.

For the record any "#+begin_XXX" construct that has no particular
meaning in Org may be treated specially by export back-ends (or ignored
altogether). It is often a way to write a specific environment.