std.typecons:toString from defineEnum

[Pedro Ferreira]

The example given in the example for defineEnum in page
http://www.digitalmars.com/d/2.0/phobos/std_typecons.html#defineEnum
does not compile.
The specific code is

import std.stdio;
import std.typecons;
mixin(defineEnum!("Openmode", "READ", "WRITE", "READWRITE", "APPEND"));
void main()
{
     Openmode m = Openmode.READ;
     string s = toString(m);
     assert(s == "READ");
     Openmode m1;
     assert(fromString(s, m1) && m1 == m);
}

But DMD (the lastest 2.x version) claims that .toString does not exist. 
Was it removed or broken? Should the bug be filed has "inconsistent 
documentation" or "broken library"?

Lastly, why not put the .toString directly onto the enum stucture? Going 
  around with this mixin is just ugly.