Download the Dart Programming Language Specification from the Ecma website:
The 2nd edition of the specification added information about the following new language features:
Implemented in 1.8. For details, see the language tour: Enumerated types.
Asynchrony support (
await, and more)
Partially implemented in 1.8. For details, see the language tour: Asynchrony support.
Deferred loading (
import ... deferred as)
Implemented in 1.6. For details, see the language tour: Lazily loading a library.
You can find both editions of the specification at Standard ECMA-408.