https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo has a couple of sections with info that seem also generally useful to anybody in our world who’s writing specs or designing APIs — specifically, these sections:

• https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#a-word-on-designing-apis
• https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo#philosophy