The lang package
The lang package is considered built-in: it is imported by default in ooc modules. There is a reason for that, however - the SDK is distributed as an ooc library itself, and as such, it has a .use file that specifies which modules should be imported.
Some of the lang package is essential, like
Class, which means that the compiler, rock, will expect them to be present, have certain names, fields and methods. However, using a custom sdk is possible, where the implementation for these can be swapped to something lighter, for example.
The Types section describes how Object, Class, and other types such as Void, Pointer, Bool, None, Cell are defined. It also discusses variable arguments.
The String section talks about string handling, the mutable variant Buffer, and formatting
The Numbers section talks about number types, either integers or floats, and the various functions available.
The Iterators section discusses how iterators are implemented, and what goes on behind a foreach.
The Exceptions section talks about default properties of exceptions, and how to extend them.
The Memory section talks about memory management, mostly just how to deal with blocks of memory rather than more high-level data structures.