What is this function call operator?

[Gary Willoughby via Digitalmars-d-learn]

On Thursday, 27 August 2015 at 16:12:35 UTC, Adam D. Ruppe wrote:
> On Thursday, 27 August 2015 at 16:03:58 UTC, Gary Willoughby 
> wrote:
>> Sorry, I mean the three dots '...' that seems to be what the 
>> documentation is referring to. Also the `isCallable` template 
>> uses it.
>
> That just means it can take whatever arguments. The 
> documentation is just saying it is callable with anything; the 
> ... is a placeholder. In the template itself, (T...) is a 
> variadic argument list, again meaning it can take anything. 
> (The reason isCallable does it though isn't to actually take 
> multiple arguments, it is so it can take any *kind* of 
> argument; a bit of a hack.)

Ah right, I get it. Thanks.