Excerpt
I didn't found official documentation about it.
The command apache2ctl -S check site-enabled*.conf + httpd.conf files and show you if the syntax is correct and the list of virtual host (and some more informations).
But It doesn't check if virtualhosts are running, you can try to stop your Apache and launch again the command, the result will be the same.
So apache2ctl -S result is based on configuration files.
I didn't found official documentation about it.
The command apache2ctl -S check site-enabled*.conf + httpd.conf files and show you if the syntax is correct and the list of virtual host (and some more informations).
But It doesn't check if virtualhosts are running, you can try to stop your Apache and launch again the command, the result will be the same.
So apache2ctl -S result is based on configuration files.