https://stackoverflow.com/questions/45466017/%c9%b5-theta-like-symbol-in-angular-2-source-code
The first thing you many notice is a lot of obscure method names, starting with the letter ɵ (Greek Theta) followed by 3 other English letters (e.g. ɵvid). The letter ɵ is used by the Angular team to indicate that some method is private to the framework and must not be called directly by the user, as the API for these method is not guaranteed to stay stable between Angular versions (in fact, I would say it’s almost guaranteed to break).