org-tag-persistent-alist AND per-file dynamic tags

[Victor A. Stoichita]

Greetings to all,

Reading the manual about setting glopal/per-file tags [1], I wonder if
it is possible to use org-tag-persistent-alist AND per-file
dynamic tags.

When using org-set-tags-command, I’d like to select from a list
comprising both:
1. the list of predefined tags in org-tag-persistent-alist
2. the list of all the tags that are already in use in the current
   buffer (some of which might not be in the persistent alist). I don’t
   want to use the #+TAGS keyword at file-level, just the list of tags
   already attached to some headline in the buffer.

The manual says:
> If you have globally defined your preferred set of tags using the
> variable org-tag-alist, but would like to use a dynamic tag list in
> a specific file, add an empty ‘TAGS’ keyword to that file

And then it says:
> If you have a preferred set of tags that you would like to use in every
> file, in addition to those defined on a per-file basis by ‘TAGS’
> keyword, then you may specify a list of tags with the variable
> org-tag-persistent-alist.

I tried to combine both behaviors by putting an empty ’TAGS’ keyword at
the top of my file. But this still only gives me the tags in
org-tag-persistent-alist. What would be the best way to add to it for
completion the tags already used in the buffer?

Regards,
Victor

Footnotes:
[1]  https://orgmode.org/manual/Setting-Tags.html