Quoted from gstellenberg:

Just a little bit of caution from somebody who's been through this before. The concept of developing pinball rules in config files is interesting and sounds great to the layman, but when you get into the details, the complexity grows and the advantages disappear. In order to make the config file 'programming' approach attractive to non-programmers, the format has to be very simple and therefore the available feature-set has to be severely limited. Otherwise, the 'programming language' you're creating becomes complex enough that it's actually easier for developers to program with python inside of MPF than with your config files on top of MPF.
There's a wealth of resources, tools, and communities for python developers, none of which exists for MPF config files. Suggesting that non-programmers learn to 'program' using YAML-style config files is probably fine for EM-style game rules, but is likely doing them a disservice for more complicated rulesets. I'd suggest doing your best to continue enhancing the feature-set in MPF to make programming rules in python easier, rather than spending time making the config file 'programming' more capable and therefore more complex. Just my $.02.
Either way, keep up the good work. Your efforts are clearly helping people understand these high level frameworks can help even non-professional programmers be successful developing new pinball games.
- Gerry
http://www.multimorphic.com