Error with constraints on a templated fuction

[Jeremy DeHaan via Digitalmars-d-learn]

On Monday, 25 August 2014 at 15:59:38 UTC, ketmar via 
Digitalmars-d-learn wrote:
> On Mon, 25 Aug 2014 15:48:10 +0000
> Jeremy DeHaan via Digitalmars-d-learn
> <digitalmars-d-learn at puremagic.com> wrote:
>
>> It compiles if I remove the 'if(typeof(T) is dchar)' section. 
>> Any thoughts?
> "is" should be used as function. here. i.e.: `if (is(T == 
> dchar))`

Is its ability to be used as a function like this documented 
anywhere? I looked and could not find it.