gnome-books has been split from gnome-documents. This allows for a
user to install just one of the apps if they want instead of being
forced to install or uninstall both In particular, AppStream clients
such as the GNOME Software app assume that there is only one app per
primary AppStream metadata file and the UI did not correctly handle
installing or uninstalling either of these apps. (It wouldn't indicate
that install/uninstall actions affect both apps.)
This was delayed because we had to update debian/copyright to fix a
gnome-books RC bug that was added by FTP Masters when this NEW source
package was accepted into Debian. gnome-books & gnome-documents were
uploaded before the soft freeze.
There will be one more upload (3.32.0) that we will want for Buster
since 3.31.90 is a pre-release. 3.32.0 is expected in about 9 days.
gnome-documents is affected by the gjs removal from s390x so we may
need manual hinting to ensure that the package migrates to Testing.
There is a very long discussion at https://bugs.debian.org/906016 about the s390x issue.