So, when I renamed Preferences/com.dcpomatic to Preferences/xcom.dcpomatic, DOM came up with a splash screen ('Setting up...'), but then an error message comes up, and quits, leaving an empty com.dcpomatic/2 folder.
So, what happens on a machine where DOM has never been installed before? Why does 2.11.16 quit upon finding no config.xml, instead of creating a default file? Are there other places with settings? In which config file does DOM store the location of the config file?

http://dcpomatic.com/manual/html/ch17.html
...this seems to be a bug in the test version, when I have no com.dcpomatic prefs folder and start up 2.10.5 release version, it comes up with the same splash screen, but successfully creates config.xml and cinemas.xml file. (Yes, I understand it may be a bad idea for a complete beginner to start with a test version

Anyway - I found out what I wanted to find out - current versions of DOM only use the config.xml and cinemas.xml within the Preferences/com.dcpomatic/2 folder. If you use project templates, there will also be a 'templates' folder within.
BTW - the recent Mac test version prefs are not compatible with 2.10.5 release, so, when switching between the two, prefs are reset (see second screenshot). Would it be useful to have a separate set of prefs for release and test versions?
- Carsten