@Kovid: Last evening I saw the info in Calibre: "5.28 created by Kovid Goyal" ... I suppose that must be you
My acknowledgement for your work!
I have used Sigil for my ebooks so far, but yesterday, I saw that Calibre offers much more features, the ebook management is better and more intuitive than Sigil.
Snippets work differently in Sigil, but that's a question of familiarity ... going to practice a little
And thank you very much for your patience with my newbie questions
Kind regards, Frank