This is needed for a case when it is necessary to create a folder in home directory of a user, to allow user read/write/remove files in the folder, but not allow to remove the folder itself (considering a regular user and not a sudoer).
In my case (i.e. RedHat) it was not enough just to put a file with root rights inside user`s folder, because the user owns the folder.
In my case if a user owns (or has all permissions on) a folder, he can remove it even with root file or empty folder inside.
I have made quite a number of experiments including playing with chown and permissions like 400, 000, o+t, 1775 etc. Initially I did not want to use chattr.
Meanwhile I have found a solution, which I share as an answer below; a variant that suits my needs so far.