A hard question about Sed command

[Alexandre Almeida]

Hello.

My name is Alexandre.

I used Sed a few years ago to edit ebooks in HTML in public domain to the
.fb3 russian extention... I added tags like <Br> in the break lines and so
on... It was an easy task...

But now I have a challenge that I can not solve using my Sed skills...

So,  I would like to ask for your help...

I posted my question in the Stackoverflow website, here is the link:

https://stackoverflow.com/q/76909889?sem=2

A nice week for all.

Alexandre.