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

[rsw0x via Digitalmars-d]

On Thursday, 21 January 2016 at 23:05:51 UTC, Dibyendu Majumdar 
wrote:
> I am puzzled as to why there is @nogc on the one hand and 
> simply nothrow on the other? Why are some attributes prefixed 
> with '@' while others aren't?
>
> Regards

"breakage" that could be fixed in a few minutes with grep
meanwhile, I typically can't go a D version without actual 
breakage that takes hours to debug.