schroot: Configuration key name 'file' is not a permitted name

I'm trying to configure a file chroot, following the "man" documentation. According to the manpage of schroot, I can use a filesystem tree archive file, and the configure an schroot to use that archive as file system. For example, in /etc/schroot.conf, the following example exists: #[lenny-file] #description=Debian lenny (oldstable) #file=/srv/chroot/lenny.tar.gz #location=/lenny #groups=sbuild So I changed it a little to: [stretch-file] description=Debian Stretch file=/tmp/jail.tar location=/jail groups=sbuild Of course, /tmp/jail.tar exists, and contains minimal bootsrapped stretch. When trying to enter the chroot with schroot -c chroot:stretch-file I get the following warning: W: line 77 [stretch-file]: Obsolete key ‘location’ used I: This option has been removed, and no longer has any effect W: line 76 [stretch-file] file: Configuration key name ‘file’ is not a permitted name. I thing that the interesting line is Configuration key name ‘file’ is not a permitted name. - How can it be? Is the man page wrong? Or do I do anything in the wrong way?