See if the docs now make more sense (I'm not entirely sure if it works like this in v1.0, but in more recent versions it should):
k : create : Mailboxes can be created (or renamed) directly under this mailbox (but not necessarily under its children, see ACL Inheritance section above)
ACL Inheritance
Every time you create a new mailbox, it gets its ACLs from the parent mailbox. If you're creating a root-level mailbox, it uses the namespace's default ACLs. There is no actual inheritance, however: If you modify parent's ACLs, the child's ACLs stay the same. There is currently no support for ACL inheritance.
The default ACLs are read from "dovecot-acl" file in the namespace's mail root directory (e.g. /var/public/Maildir).
Thank you very much for your time and effort. During the time between my question and your answer, I just (gratefully) have wondered why the creation of nested folders / mailboxes worked like expected whereas the docs (in my interpretation) stated that it shouldn't work...
Now, it's understandable even for complete newbies.
Regards,
Peter
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