Actually the following modules are part of Phobos:
- the gc package (gc2/)
- invariant.d
- array.d
- arraycat.d
- arraycast.d
- assert.d
- cast.d
- invariant.d
- ti_*.d
- etc...

These modules are not intended to be directly imported,
but to be used through D syntax:
>>> char[] a = "hel", b = "lo", c;
>>> c = a ~ b; //this is a call to the function arraycat._d_arraycat()

I think these modules shouldn't be part of Phobos,
but should be a separate library to prevent the programmer
to inadvertently import those. =)

I do like a lot the possibility to modify the D runtime library to
make it suit the programmer's needs. I can even modify the garbage
collector to make it malloc the memory, that is to make new work as in C++,
as somebody wanted. ;-)
Anyway, this should be documented. And there should be the _new() and
_delete() functions somewhere that call the gc by default.

-Dario