since when was this valid syntax?

[Maxim Fomin]

On Saturday, 8 September 2012 at 16:00:44 UTC, Timon Gehr wrote:
> On 09/08/2012 04:11 PM, Ellery Newcomer wrote:
>> alias enum int e;
>
> It is valid according to the grammar and DMD ignores 
> meaningless attributes.
>
> scope shared @disable @trusted package final override 
> deprecated extern __gshared synchronized pure nothrow ref 
> static abstract immutable alias auto final override deprecated 
> extern __gshared synchronized enum pure nothrow ref static 
> abstract @safe @disable scope int e;

How dmd's parser is written if it allows such things?