@meme
Thanks very much for your quick and informative reply.
nnbsp seems to get better and better support.
For this version of Sigil (0.7.3) this new and unannounced display of nnbsp in Sigil confused me and made me look for an -unexistent and unneeded- solution quite a long time.
For your information, a bug report has been sent about the display of nnbsp on Bugzilla for LibreOfice users (odt files).
https://bugs.freedesktop.org/show_bug.cgi?id=67669
It is probable that this conversion in Code view of nnbsp into a plain white space will confuse some other people. It would be probably better to use some kind of greyed character. Hopefully, this will be for Qt 6. ;-)