rsync - newbie question

[Richard Owlett <rowlett@cloud85.net>]

In another thread it was suggested that I use:    > rsync -avzh --delete 
-n <fromdirectory> <todirectory>

I tried it and got ~200 error messages of form:

> file has vanished: "/proc/10/exe"

> file has vanished: "/proc/10/task/10/exe"

> file has vanished: "/proc/101/exe"

> file has vanished: "/proc/101/task/101/exe"

> file has vanished: "/proc/10146/exe"

> file has vanished: "/proc/10146/task/10146/exe"

> file has vanished: "/proc/10300/cwd"

> file has vanished: "/proc/10300/root"

> file has vanished: "/proc/10300/exe"

Spot checking properties of those showed that although they had multiple 
sub-directories the content was "0 bytes".

Browsing [https://manpages.debian.org/stretch/manpages/proc.5.en.html] 
implied that excluding everything under /proc would be reasonable.

Am I correct?
TIA