mri

All Ruby interpreters follow the same Ruby syntax?

Do all Ruby interpreters follow the same Ruby syntax defined in www.ruby-lang.org? MRI YARV Rubinius JRuby IronRuby Cause it is the interpreter that defines the Ruby language. Does that mean one interpreter could add a feature/syntatic sugar that other interpreters haven't? If that is the case, do all interpreters have their own API...