StringStream is sort-of an enumerator on a String, with a
InputStream interface.
instance (id) with String string;
string.
String string;
String we're streaming.
int next;
protected id init String s;
byte read;
int read;
int
readRange (int, int) (start, num)
into MutableByteArray buffer;
(start, num) from the string into the buffer.