TL;DR: Plan to add features to HTML export, do I add them in the
       built-in HTML exporter (as upstream contribution) ? Or as a
       downloadable derived backend ? Which on do you prefer ?


Hello,

I plan to use Org-publish to create a website from Org-mode files. And I
would have some features that are not provided by the built-in HTML
exporter.

To add theses features, my first plan was to customize an org-publish
project. Using a custom preamble function, a custom completion function
and some new export options added to "org-export-options-alist".

It's still a work in progress, but the more feature I add, the more I
think I need to add them in an export backend.

So, my second plan is to create an export backend, derived from the
built-in HTML exporter.

But maybe you would prefer that I add these new features as a
contribution to the built-in HTML exporter ?

Here is what I plan to add, on each generated webpage, compared to what
the built-in HTML exporter already provide:

- A side panel containing:
  - A site web name and/or logo
  - A search field for an local search engine
  - A main navigation menu, built from a dedicated org-mode file
- A more "modern" look
- More special blocks available like:
  - A question/answer bloc, where the answer is hidden
  - Important, warning and tip blocks
  - A generic hide-show bloc
- Tab to select which content to see
- Bibliography on a dedicated webpage when using org-publish
- A button to download the Org-mode file source of a webpage
- Possibility to set the home page, when there is no index.org
  
As say above, I started it as a custom org-publish
project. You can found my work in progress here:
https://framagit.org/SebGen/org-documentation-template

For now, the search engine use the software Pagefind:
https://pagefind.app

And the menu is made from an org-mode file where first level heading
become menu item and links are simple org-mode links.


Best regards

-------
Gendre Sébastien