Most of the documentation is a snapshot of the old Namesys site (archive.org, 2007-09-29).
There was also a Reiser4 Wiki (archive.org, 2007-07-06) once on pub.namesys.com.
Reiser4 development appears to have stalled and ReiserFS is deprecated and scheduled to be removed from mainline Linux in 2025.
Bugs
From Reiser4 FS Wiki
OBSOLETE CONTENT
This wiki has been archived and the content is no longer updated.
If you find a bug, please report it to the mailinglist. Already reported bugs can be found on the kernel.org Bugzilla