This was interesting and caused me to go off on a neat little tangent too.

I was curious about the VALUE declaration in:

    struct RString {
      long len;
      char *ptr;
      VALUE shared;
    };

From the Hacker Guide referenced, I found this definition:

    typedef unsigned long VALUE;

This is then casted, when needed, to a pointer to whatever type of struct you are dealing with. How does that work?

Well, on a 32-bit machine, if I'm correct in my reading, an unsigned long is 4 bytes in size and can contain these numbers: 0 to 4294967295

That last number is 4 gigabytes, which is the size of byte-addressable memory on a 32-bit machine. So VALUE can point anywhere. Neat!