An answer on Unix & Linux Stack Exchange led me to look at the manual page for
console devices on Linux operating systems.
It turned out that because of a lack of coödination, an entire family of Linux operating systems lost its manual page for these devices years ago.
The Debian people noticed the omission in 2014 and updated Debian to install the manual page from the Linux Man-Pages Project.
And the people from that project updated their project to delete that manual page because "Debian and derivatives don't install this page" and "Debian no longer carries it".
So I made some:
The result of converting the DocBook XML to HTML with
xmlto looks like