Why do some attributes start with '@' while others done't?

[Dicebot via Digitalmars-d]

On Friday, 22 January 2016 at 03:18:29 UTC, Timon Gehr wrote:
> On 01/22/2016 03:20 AM, Dicebot wrote:
>> I'd definitely place something like `@safe` in type 
>> constructors
>
> @safe(int) ?

Normally I rely on this definition:

feature .. builds new types from old ones 
(https://en.m.wikipedia.org/wiki/Type_constructor)

That matches my intuitive expectations. I.e. plain 'extern' is a 
storage class because for `const int x; extern int y;` type of y 
is still plain into but x is const(int)

@safe functions do have distinct type thus I'd expect it to be 
type qualifier/constructor. However D seems to use different 
classification that isn't documented anywhere.