Isn't __traits part of the language?

[simendsjo]

Rationale (http://digitalmars.com/d/2.0/rationale.html) says:
"""Why not use operator names like __add__ and __div__ instead of opAdd, 
opDiv, etc.?

__ keywords should indicate a proprietary language extension, not a 
basic part of the language. """


But traits is explained under the language spec, 
http://digitalmars.com/d/2.0/traits.html.


Can I expect traits to exist for all compiler implementations, or just dmd?