Inasmuch as we are still hashing out the fine points, I'd like to start a rhizopod spec, so that I can continue my pythoncad<->rhizopod code, and maybe use for validation. Please check out a partial draft at http://dan-davis.com/cds/rhizopod_spec.yml One issue I'm not clear on is making some attributes optional. Things like units and color can either be optional, or mandatory with a link to the governing file, if set globally. ie color attribute in a circle can be specified, to override a global value, can be absent to indicate global value should be used, or be present with a 'bystyle', 'bylayer', or '5.yml' attribute.