template instance template 'appender' is not defined

[Assembly via Digitalmars-d-learn]

So after a while without write any D code (such a sad time) I'm 
back. I needed to use appender but it returned a compile error:

> template instance template 'appender' is not defined

I've imported the std.format module but it still doesn't works. 
What changed? did this moved to somewhere else or what? the 
documentation still says that it's in the std.format module 
(http://dlang.org/phobos/std_format.html). I guess I need to read 
the break changes log since the version I'm using?

My machine: Windows 8.1 and dmd version v2.066.0.