To display websites under #YunoHost, a special #My_Webapp application needs to be installed for each configured domain. Okay, I get that. Of course, there are pitfalls, but that's probably inevitable.
My first attempt with re-form.eu has been a failure so far. But with the knowledge I gained, I managed to get clean-web.org up and running successfully. At least.
This blog, as you know, relies on #ssi, or #shtml pages. This has to be specifically enabled in the #nginx web server, which I did. I don't know if it's in the right place or in the right way. I have the information from the original nginx documentation, and the server didn't report any errors after reloading. Furthermore, there's an #htaccess file in the web directory that specifies index.shtml as the first file to be launched. Nevertheless, only a 404 page appears.