ADDENDUM ...
I used root to create the /data/svn directory. Then, anticpiating
problems, I did a chmod to make it writable to all.
Later I ran svnadmin create /data/svn/sample and it created an entire
repository directory tree under /data/svn. I don't remember but I
probably ran it as root.
I just now noticed that /data/svn/sample and all the sub-directories and
files therein are owned by root and, usually, writable only by root.
This is probably going to cause problems for Apache / mod_dav_svn which,
of course, runs as the 'apache user' ("www-data") instead of root.
Where did I go wrong? The manual talks about commands but does not seem
to talk about what user is executing the command. Do I have to run
svnadmin as www-data? Is there a way to create a repository using my
browser?