[Dovecot] Syntax to specify sdbox: mail_location path?

[mephistopheles at operamail.com]

I'm implementing sdbox.

In conf.d/10-mail.conf, with "maildir:"

 mail_location = maildir:/my_mailbox_path/%d/%n

mail gets stored in /my_mailbox_path/%d/%n/new/

With "sdbox:"

 mail_location = sdbox:/my_mailbox_path/%d/%n

mail gets stored in /my_mailbox_path/%d/%n/mailboxes/INBOX/dbox-Mails.

How do I get rid of the '/mailboxes/' and '/dbox-Mails/' path components
so sdbox stores in:

	/my_mailbox_path/%d/%n/INBOX

@ wiki2.dovecot.org/MailboxFormat/dbox#Alternate_storage points out that
'ALT=' can change the *lookup* location, and messages can be *moved* to
ALT storage using 'doveadm altmove'.

Unclear what TAGS are available/used for 'sdbox'.